Method and apparatus for test connectivity, communication, and control

ABSTRACT

Functional circuits and cores of circuits are tested on integrated circuits using scan paths. Using parallel scan distributor and collector circuits for these scan paths improves test access of circuits and cores embedded within ICs and reduces the IC&#39;s power consumption during scan testing. A controller for the distributor and collector circuits includes a test control register, a test control state machine and a multiplexer. These test circuits can be connected in a hierarchy or in parallel. A conventional test access port or TAP can be modified to work with the disclosed test circuits.

This application is a divisional of application Ser. No. 14/547,781,filed Nov. 19, 2014, currently pending;

Which was a divisional of application Ser. No. 14/087,764, filed Nov.22, 2013, now U.S. Pat. No. 8,924,804, issued Dec. 30, 2014;

Which is a divisional of application Ser. No. 13/858,625, filed Apr. 8,2013, now U.S. Pat. No. 8,621,300, issued Dec. 31, 2013;

Which was a divisional of application Ser. No. 13/604,864, filed Sep. 6,2012, now U.S. Pat. No. 8,438,441, issued May 7, 2013;

Which was a divisional of application Ser. No. 13/272,720, filed Oct.13, 2011, now U.S. Pat. No. 8,296,614, issued Oct. 23, 2012;

Which was a divisional of application Ser. No. 12/956,828, filed Nov.30, 2010, now U.S. Pat. No. 8,065,577, issued Nov. 22, 2011;

Which was a divisional of application Ser. No. 11/560,143, filed Nov.15, 2006, now abandoned;

Which was a divisional of application Ser. No. 10/114,193, filed Apr. 2,2002, now U.S. Pat. No. 7,155,646, issued Dec. 26, 2006;

Which was a divisional of application Ser. No. 09/248,504, filed Feb.10, 1999, now U.S. Pat. No. 6,378,093, issued Apr. 23, 2002;

Which claimed priority to provisional application Ser. No. 60/074,264,filed Feb. 10, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to testing of integrated circuits withscan paths and particularly relates to testing integrated circuits withparallel scan distributors and collectors controlled by a controllerthat includes a state machine.

2. Description of the Related Art

Cost effective testing of today's complex integrated circuits isextremely important to semiconductor manufacturers from a profit andloss standpoint. The increases in complexity of state-of-the-artintegrated circuits is being accompanied by an ever increasingdifficulty to test the integrated circuits. New test techniques must bedeveloped to offset this increasing integrated circuit test cost,otherwise further advancements in future integrated circuit technologymay be blocked. One emerging technology that is going to accelerate thecomplexity of integrated circuits even more is intellectual propertycores. These cores will provide highly complex pre-designed circuitfunctions such as; DSPs, CPUs, I/O peripherals, memories, and mixedsignal A/D and D/A functions. These cores will exist in a library andcan be selected and placed in an integrated circuit quickly to provide acomplex circuit function. The low cost testing of integrated circuitsthat contain highly complex core functions will be a significantchallenge.

SUMMARY OF THE INVENTION

The disclosed circuits provide a description of a controller for usewith the parallel scan distributor and collector circuits. Thecontroller has a test control register, a test control state machine anda multiplexer. The controller also has inputs and outputs for connectionto additional controllers in a hierarchical or parallel arrangement. Thecontroller is also programmable to provide different types of testcontrol for testing different types of circuits.

The disclosed parallel scan distributor and collector circuits provide alow power method of scan testing combinational logic within an IC byallowing scan test communication to occur over a larger number ofshorter length scan paths.

With a synchronizer and delay circuit, the disclosed test circuits canfurther reduce the power needed to test the integrated circuits. Thetest circuits disclosed can be used to test functional combinatoriallogic, random access memory, and digital to analog and analog to digitalcircuitry. Conventional IEEE 1149.1 test access port or TAP circuits canbe modified to operate with the disclosed scan distributor andcollectors circuits and controllers.

BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS

FIG. 1 depicts an integrated circuit.

FIG. 2 is a block diagram of a known parallel scan path testarrangement.

FIG. 3 is a block diagram of a parallel scan path test arrangementaccording to the present invention.

FIG. 4 is a block diagram of the scan path test arrangement of FIG. 3further including a test controller according to the present invention.

FIG. 5 is a flow chart illustrating operation of the test controller andscan path arrangement of FIG. 4.

FIG. 6 is a flow chart illustrating an alternate operation of the testcontroller and scan path arrangement.

FIG. 7 depicts an integrated circuit that includes an embedded core.

FIG. 8 is a block diagram of a scan test circuit and controllerarrangement for testing the integrated circuit and core of FIG. 7according to the present invention.

FIG. 9 depicts an integrated circuit including an embedded core, inwhich the embedded core itself includes an embedded core.

FIG. 10 is a block diagram of a scan test circuit and controllerarrangement for testing the integrated circuit and embedded cores ofFIG. 9 according to the present invention.

FIG. 11 is a block diagram of a hierarchical connection between scantest circuit arrangements according to the present invention.

FIG. 12 is a block diagram of an arrangement of scan test circuits andcontrollers using multiplexer circuitry according to the presentinvention.

FIG. 13 depicts an integrated circuit.

FIG. 14 is a block diagram of an arrangement of scan test circuits andcontrollers for the integrated circuit of FIG. 13.

FIGS. 15A and 15B are block diagrams of a controller used in the scantest circuits.

FIG. 16 is a flow chart of states used in the controller of FIG. 15.

FIG. 17 is a block diagram of controllers arranged in a hierarchy.

FIG. 18 is a block diagram of controllers connected in a multiplexedarrangement.

FIG. 19 is a block diagram of controllers arranged in parallel.

FIGS. 20A and 20B are block diagrams of integrated circuits under testand test drivers and receivers.

FIGS. 21A and 21B are block diagrams of scan path circuits andrepresentations of capacitive loadings.

FIGS. 22A and 22B are, respectively, a block diagram of a serialconnection of clock signals and a timing diagram of the clock signalsoccurring in series.

FIG. 23A-1 is a block diagram of a random access memory device includingparallel scan distributor and collector circuits.

FIG. 23A-2 is a flow chart of states used to test a random access memorydevice.

FIG. 23B-1 is a block diagram of a digital to analog converter includingparallel scan distributor circuits.

FIG. 23B-2 is a flow chart of states used to test a digital to analogconverter.

FIG. 23C-1 is a block diagram of an analog to digital converterincluding parallel scan collector circuits.

FIG. 23C-2 is a flow chart of states used to test an analog to digitalconverter.

FIG. 24 is a block diagram of an integrated circuit with mixed signalcores.

FIG. 25A is a block diagram of a conventional test access port.

FIG. 25B is a block diagram of a modified test access port.

FIG. 26 is a block diagram of a modified test access port and testcontroller joined together.

DETAILED DESCRIPTION

In FIG. 1, integrated circuit 100 comprises a semiconductor substrate102 with bond pads 104 and functional circuitry 106. To expeditetesting, an integrated circuit's functional circuitry 106 can bearranged into many parallel scan paths, each scan path having a serialdata input and serial data output. Having many short parallel scanpaths, versus one long continuous scan path, is preferred since itreduces the time it takes to shift test data in and out. Each parallelscan path's serial data input and output can be connected to a bond pad104 to allow a tester to input test data to and output test data fromall scan paths concurrently. Parallel scan design references includeFIG. 18-3 of Chapter 18 of 1990 IEEE Publication “The Test Access Portand Boundary Scan Architecture” by Colin Maunder, and FIG. 14 a of U.S.Pat. No. 5,526,365 to Whetsel.

In FIG. 2, known parallel scan path 200 has a serial data input at pad202 and a serial data output at pad 204. Known parallel scan path N 206has a serial data input at pad 208 and a serial data output at pad 210.In the circuits of FIG. 2, N scan paths will require use of 2.times.Nbond pads for serial data input and serial data output. While some bondpads will be used to supply control to the scan paths and for power andground, a majority of the bond pads may be used for scan path serialdata input and output. The number of available bond pad pairs will limitthe number of scan paths that can be accessed in parallel.

The scan cycle time of the conventional scan path arrangement of FIG. 2can be expressed by (L+1)T, where L is the scan path length throughwhich stimulus and response test patterns are shifted during each scancycle, 1 is the capture step required to input response data from thefunctional logic under test into the scan path, and T is the period ofthe scan clock. Using this equation, for example, the scan cycle timefor a scan path having a length (L) of 1000 bits is (1000+1)T, or 1001T.The test time equals “scan cycle time” times “the number of testpatterns”.

In FIG. 3, scan test circuit 301 includes a scan distributor 300, scanpaths 324 through 342 and scan collector 344. Parallel scan distributorcircuit 300 forms a data input amplification circuit connected betweenbond pad 302 and data inputs 304 through 322 to ten plural scan paths324 through 342, of which only the first and last are depicted forclarity of the drawing. Parallel scan collector circuit 344 forms anoutput amplification circuit connected between the data outputs 346through 364 of plural scan paths 324 through 342 and bond pad 366.

Scan test circuit 367 includes a scan distributor 368, scan paths 392through 410 and scan collector 412. In a like manner, parallel scandistributor circuit 368 forms a data input amplification circuitconnected between bond pad 370 and data inputs 372 through 390 to tenplural scan paths 392 through 410, of which only the first and last aredepicted for clarity of the drawing. Parallel scan collector circuit 412forms an output amplification circuit connected between the data outputs414 through 432 of plural scan paths 392 through 410 and bond pad 434.

Scan paths 324 through 342 form one group of scan paths connectedbetween scan distributor circuit 300 and scan collector circuit 344.Scan paths 392 through 410 form another group of scan paths connectedbetween scan distributor circuit 368 and scan collector circuit 412.

In FIG. 3, the parallel scan distributor provides a data inputamplification circuit located between a bond pad and data inputs toplural scan paths. The parallel scan collector provides a data outputamplification circuit located between the data outputs of the pluralscan paths and a bond pad. This is different from the conventionalparallel scan path arrangement depicted in FIG. 2 in which each scanpath's data input is directly connected to a bond pad and each scanpath's data output is directly connected to a bond pad. Therefore, thedata amplification capability of the present invention is understood bycomparing FIG. 2 and FIG. 3.

The conventional parallel scan path arrangement of FIG. 2 thus ismodified by the insertion of parallel scan distributor circuits andparallel scan collector circuits. The scan distributor circuits 300, 368are basically serial-input parallel-output shift registers, and the scancollector circuits 344, 434 are basically parallel-input serial-outputshift registers. While the parallel input and output width of the scandistributor and collector circuits can be of any bit width, thedistributor and collector circuits 300, 344, 368 and 412 have 10 bitwide parallel inputs and outputs that provide one bit input and outputto the respective parallel scan paths.

The scan input modifications of the FIG. 2 arrangement include: (1)disconnecting the bond pads from scan paths 1-N, (2) inserting the scandistributor circuits, (3) connecting the bond pads to the serial inputsof the scan distributor circuits, and (4) connecting each paralleloutput of the scan distributor circuits to a respective input of thescan paths. The scan output modifications of the FIG. 2 arrangementinclude: (1) disconnecting the bond pads from scan paths 1-N, (2)inserting the scan collector circuits, (3) connecting the bond pads tothe serial outputs of the scan collector circuits, and (4) connectingthe output of each scan path to a respective parallel input of the scancollector circuits.

The scan path modifications of the FIG. 2 arrangement include: (1)dividing each scan path 1-N into a group of individual shorter lengthscan paths, each preferably being of equal length, and in which thenumber of individual scan paths of each group equals to the number ofparallel inputs and outputs (10) of the scan distributor and scancollector circuits, (2) connecting the serial data input of each scanpath of each group to a parallel output of a respective scan distributorcircuit, and (3) connecting the serial data output of each scan path ofeach group to a parallel input of a respective scan collector circuit.

With 10 bit deep scan distributor and collector circuits, the number ofindividual scan paths in each group is equal to ten. If the scan paths200 and 206 of FIG. 2 were each 1000 bits long, the above partitioningwould convert each 1000 bit scan path into a group of ten 100 bit scanpaths.

In FIG. 4, integrated circuit 446 includes scan test circuits 448. Onescan distributor 450 and scan collector 452 pair provide access to 10parallel scan paths 454 through 472. Each of the 10 parallel scan pathsconnects to combinational logic 474 in functional circuitry 106. Thecombinational logic 474 is tested by inputting test stimulus andoutputting test response through the parallel scan paths 454 through472. While stimulus input and response output connections are shown onlybetween combinational logic 474 and parallel scan path 1 454, all ten ofthe parallel scan paths 454 through 472, respectively, are similarlyconnected to combinational logic 474.

A controller 476 connects to the scan distributor circuit 450, parallelscan paths 1-10 454 through 472 and scan collector 452, as well as allother scan distributors, parallel scan paths, and scan collectors in theintegrated circuit by leads 482. Controller 476 controls the testoperation of the scan distributor circuits, parallel scan paths 1-10 454through 472 and scan collector 452, as well as all other scandistributors, parallel scan paths, and scan collectors in the integratedcircuit. The controller 476 connects to bond pads 478 and 480 for accessand control by a source external to the integrated circuit, such as awafer or integrated circuit tester.

When the integrated circuit's functional circuitry is configured fortesting, all functional registers (flip/flops or latches) in theintegrated circuit are converted into scan registers that form theparallel scan paths shown. Also, during test configuration, allcombinational logic in the integrated circuit that was associated withthe functional registers remains associated with the scan registersafter the conversion. This conversion of an integrated circuit'sfunctional circuitry into scan paths and combinational logic is wellknown.

The combinational logic 474 is tested by receiving test stimulus datafrom the parallel scan paths 454 through 472 and outputting testresponse data to the parallel scan paths 454 through 472. The teststimulus data applied to the combinational logic 474 from the parallelscan paths is input to the parallel scan paths via the scan distributor450. The test response data received into the parallel scan paths fromthe combinational logic is output from the parallel scan paths via thescan collector 452. During test, the controller 476 operates the scandistributor 450, parallel scan paths 454-472, and scan collector 452 totest the combinational logic 474. Simultaneous with this test, thecontroller 476 also operates other scan distributors, parallel scanpaths, and scan collectors of the integrated circuit to test furthercombinational logic within the integrated circuit.

In FIG. 5, the flow chart illustrates one example of the controlleroperating the scan distributor, parallel scan paths, and scan collectorof FIG. 4 during testing of the integrated circuit's combinationallogic. Initially, the controller will be in the start test state waitingfor a signal to start testing. In response to a start test signal, thecontroller executes the following steps. The step numbers correspond tothe state numbers in the diagram of FIG. 5.

1 Step Number Operation 501 Test to see if start test has occurred. No,goto 501. Yes, goto 502. 502 Configure functional circuitry into testmode, goto 503 503 Capture response data outputs from all parallel scanpaths (PSPs) into scan collector (PSC), goto 504 504 Shift scandistributor and collector ten times to load stimulus data intodistributor and unload response data from collector, goto 505 505 Shiftscan paths one time to load scan paths with test stimulus data from scandistributor, goto 506 506 Test to see if parallel scan paths (PSPs) havefilled with the test stimulus pattern No, goto 503 Yes, goto 507 507Test to see if end of test has occurred No, goto 508 Yes, goto 509 508Capture response pattern from combinational logic into parallel scanpaths (PSPs), goto 503 509 End of test, configure IC circuitry intonormal mode, goto 501

Following the end of test step 507, the test is complete and thecontroller configures the functional circuitry back into its normalmode, then goes to and remains in the start test state 501 until anotherstart test signal occurs. During the test, a tester supplies stimulusdata to the scan paths via the serial to parallel operation of the scandistributors, and receives response data from the scan paths via theparallel to serial operation of the scan collectors. The tester comparesthe response data it receives from the scan collectors to expectedresponse data to determine if the test passes or fails. Alternately,during test the tester may compress the response data it receives fromthe scan collectors into signatures and then compare signatures at theend of test to expected

In FIG. 6, an example of another controller flow chart illustrates howthe decision states 506 and 507 of FIG. 5 may be merged into state 605of FIG. 6 to streamline the test execution flow. In FIG. 6, state 605executes the shift operation that moves data from the scan distributorsinto the scan paths, then executes decision states to determine whetherthe next state will be state 503, 508, or 509. Merging the decisionstates into state 605 is possible because the decisions regarding thefull/not full status of the scan paths and the end of test are easilypredictable conditions.

2 Step Number Operation 501 Test to see if start test has occurred No,goto 501 Yes, goto 502 502 Configure IC circuitry into test mode, goto503 503 Capture response data outputs from all parallel scan paths intoscan collectors, goto 504 504 Shift scan distributors & scan collectorsten times to load stimulus data into scan distributors and unloadresponse data from scan collectors, goto 605 605 Shift scan paths onetime to load scan paths with test stimulus data from scan distributors,then If scan path is not filled, goto 503 If scan path is filled & notend of test, goto 508 If scan path is filled & end of test goto 509 508Capture response pattern from combinational logic into scan paths, goto503 509 Configure IC circuitry into normal mode, goto 501

While the test data input and output bandwidth of the scan paths 454through 472 is reduced by the serial to parallel translation in scandistributor 450 and parallel to serial translation in scan collector 452that occurs for each datum shifted into and out of the parallel scanpaths. The overall test time however is comparable to the conventionalparallel scan test times for the circuits of FIG. 2. The reason for thisis that scan distributor and scan collector circuits enable test data tobe communicated to a larger number of shorter length parallel scanpaths, whereas the conventional parallel scan arrangement of FIG. 2communicates test data to a lesser number of longer length scan paths.

The scan cycle time of the scan distributor and scan collectorarrangement of FIG. 4, using the FIG. 6 controller operation steps, canbe expressed by equation ((D+2)L+1)T, where: (D+2) is the scan depth (D)of the scan distributor and scan collector circuits shifted, step 504;plus 2, the shifting of data between scan distributor and scan paths instep 605, and between scan collector and scan paths in step 503; L isthe scan path length through which data is shifted during each scancycle; plus 1, the capture step 508 required to input data from thecombinational logic into the scan paths; and T is the period of the scanclock.

For the purpose of illustrating a comparison of the scan cycle timesbetween the conventional path arrangement of FIG. 2 and the scandistributor and scan collector scan path arrangement of FIG. 4, the L inthe scan distributor and scan collector scan cycle time equation abovecan be expressed in terms of the L in the conventional scan cycle timeequation. As previously described in regard to FIG. 3, a conventionalscan path having a length (L) can be converted into a group of tenindividual scan paths each having a length of L/10, when using 10 bitscan distributor and scan collector circuits. Converting the originalconventional scan path of FIG. 2 into an equivalent scan distributor andscan collector scan path arrangement does not modify the stimulus andresponse connections to the combinational logic, it simply partitionsthe single conventional scan path into an equivalent group of shorterlength scan paths. Therefore, for the purpose of comparing scan cycletimes between the conventional scan path arrangement of FIG. 2 and aconverted, but equivalent, stimulus and response connection, scandistributor and scan collector scan path arrangement of FIG. 4, L/10 issubstituted for L in the scan distributor and scan collector scan cycletime equation above.

This results in a scan distributor and scan collector scan cycle timeequation of: ((D+2) (L/10)+1)T, or ((10+2) (L/10)+1)T, or (1.2L+1)T,where: L equals the bit length of the original scan path of FIG. 2, andD equals the depth (i.e. 10 bits) of the scan distributor and scancollector circuits. Substituting L=1000 into the conventional scan pathequation, (L+1)T, of FIG. 2 and scan distributor and scan collectorequation, (1.2L+1)T, above, results in 1001T and 1201T, respectively. Incomparing 1001T to 1201T, it is seen that the conversion of theconventional scan path arrangement into an equivalent scan distributorand scan collector scan path arrangement only extends the scan cycletime by approximately 16.6%, in this example.

The scan distributor and scan collector scan cycle time advantageouslyapproaches the conventional scan test time as the depth of the scandistributor and scan collector circuits increase, since test data may becommunicated to a larger number of shorter length parallel scan paths.For example, with 40 bit deep scan distributor and scan collectorcircuits connected to forty 25 bit scan paths, converted from the FIG. 2scan path as described above, the scan distributor and scan collectorscan cycle time becomes (40+2) (L/40)+1)T, or (1.05L+1)T, which extendsthe scan cycle time by approximately 4.7% compared to the conventionalscan cycle time. For identical combinational logic being tested, thenumber of scan cycles required to apply the test patterns is the samefor both the scan distributor and scan collector and conventional scanpath arrangements. The integrated circuit test time will therefore beextended in proportion to the scan cycle time extension.

In FIG. 7, an integrated circuit 700 contains within its functionalcircuitry 702 a complex core circuit 704, such a DSP. The integratedcircuit's functional circuit 702 contains other circuits besides thecore. Integrated circuit 700 includes peripheral bond pads 706 and corecircuit 704 includes its own set of peripheral terminals 708. In thisexample, both the integrated circuit 700 and core 704 have been designedto include the previously described invention comprising scandistributor and scan collector circuits, parallel scan paths, and thecontroller 476.

In FIG. 8, the integrated circuit 700 includes functional circuit andcore circuit scan distributor and scan collector architectures. The viewis simplified in that it depicts only one exemplary pair of scandistributor and scan collector circuits for each of the functional andcore circuits.

In FIG. 8, functional scan test circuits 801 associate with functionalcircuits 702. Parallel scan distributor circuit 800 forms a data inputamplification circuit connected between bond pad 802 and data inputs 804through 822 to ten plural scan paths 824 through 842, of which only thefirst and last are depicted for clarity of the drawing. Parallel scancollector circuit 844 forms an output amplification circuit connectedbetween the data outputs 846 through 864 of plural scan paths 824through 842 and bond pad 866. Bond pads 802 and 866 are part ofperipheral bond pads 706 of the functional circuits 702.

A controller 876 connects to the scan distributor circuit 800, parallelscan paths 1-10 824 through 842 and scan collector 844, by leads 882.Controller 876 controls the test operation of the scan distributorcircuit 800, parallel scan paths 1-10 824 through 842 and scan collector844. The controller 876 connects to bond pads 878 and 880 for access andcontrol by a source external to the integrated circuit 700, such as awafer or integrated circuit tester. Bond pads 878 and 880 are part ofperipheral bond pads 706.

In core circuits 704, core scan test circuits 901 associate with corecircuits 704. Parallel scan distributor circuit 900 forms a data inputamplification circuit connected between terminal 902 and data inputs 904through 922 to ten plural scan paths 924 through 942, of which only thefirst and last are depicted for clarity of the drawing. Parallel scancollector circuit 944 forms an output amplification circuit connectedbetween the data outputs 946 through 964 of plural scan paths 924through 942 and terminal 966. Terminals 902 and 966 are part of corecircuit terminals 708 of the core circuits 704.

A controller 976 connects to the scan distributor circuit 900, parallelscan paths 1-10 924 through 942 and scan collector 944, by leads 982.Controller 976 controls the test operation of the scan distributorcircuit 900, parallel scan paths 1-10 924 through 942 and scan collector944. The controller 976 connects to terminals 978 and 980 for access andcontrol by controller 876 over leads 984 and 986. Terminals 978 and 980are part of core circuit terminals 708.

Scan distributor 800 has a serial output on lead 884 connecting to oneinput of multiplexer 886. The other input of multiplexer 886 receives asignal FI. The sole output of multiplexer 886 connects on lead 888 toterminal 902. Terminal 966 connects to the sole input of demultiplexer890. One output of demultiplexer 890 on lead 892 connects to a serialinput of scan collector 844. The other output of demultiplexer 890connects to a signal FO. Controller 876 connects to the multiplexer 886on lead 894 and connects to the demultiplexer 890 on lead 896.

In the integrated circuit 700, the scan distributor 800 and scancollector 844 circuits are associated with the I/O bond pads for theintegrated circuit 700. In the core 704, the scan distributor 900 andscan collector 944 circuits are associated with the I/O terminals forthe core circuits 704. The scan distributor 800 and scan collector 844circuits are the same as described in regard to FIG. 4, except that thescan distributor circuit 800 has been provided with a serial output 884and the scan collector 844 circuit has been provide with a serial input892. The core's scan distributor 900 and scan collector 944 circuits arethe same as scan distributor 800 and scan collector 844 circuits withtwo exceptions: they are associated with the core's terminals 902 and966 and they have no serial output 884 or serial input 892.

A multiplexer 886, or other type of connection circuit, is provided ateach core terminal that has a scan distributor, and a demultiplexer 890,or other type of connection circuit, is provided at each core terminalthat has a scan collector. The multiplexer allows inputting either afunctional input signal or test input to the core terminal. Thedemultiplexer allows outputting either a functional output signal ortest output from the core terminal.

The test input to the multiplexer 886 comes from the serial output ofthe integrated circuit's scan distributor circuit 800, and the testoutput from the demultiplexer 890 goes to the serial input of theintegrated circuit's scan collector circuit 844. The functional inputand output, FI and FO, are connected to neighboring circuits within theintegrated circuit. During normal mode, the integrated circuit'scontroller 876 controls the multiplexers and demultiplexers at the coreterminals to input and output the functional signals. In test mode, thecontroller 876 controls the multiplexers and demultiplexers to input andoutput test signals.

Controller 976 is not directly connected to the peripheral bond pads 878and 880 as is controller 876. Rather, controller 976 for the corecircuits is connected indirectly to the peripheral bond pads via thecontroller 876. Controller 876 has authority over the core's controller976 in that controller 876 can enable, disable or modify the operationmodes of controller 976. However, during test the controllers mayoperate together to synchronize the operation of the scan distributorand scan collector circuits of the integrated circuit and core.

As will be seen in embodiments to be described, this controllerinterconnect technique is maintained between controllers that arearranged hierarchically within an integrated circuit. Also, theauthority of a higher level controller over a lower level controller ismaintained in controllers arranged within a hierarchy. Furthermaintained is the ability of hierarchical controllers to synchronizethemselves during test so that the operation of all hierarchicallylinked scan distributor and scan collector circuits, associated with thecontrollers, occur synchronously.

Testing, using the integrated circuit and core scan distributor and scancollector circuits of FIG. 8, is the same as previously described forthe circuits of FIG. 4 with two exceptions. The serial data input to thecore's scan distributor circuit 900 passes through the integratedcircuit's scan distributor circuit 800 and the serial data output fromthe core's scan collector circuit 944 passes through the integratedcircuit's scan collector circuit 844. Three types of testing can occuron the integrated circuit 700: (1) testing of the integrated circuit'sfunctional non-core circuitry, (2) testing of the core circuitry, and(3) simultaneous testing of both the integrated circuit's non-corecircuitry and the core circuitry.

When the integrated circuit's non-core circuitry is being tested, butthe core is not being tested, the core's controller 976 is disabled bythe integrated circuit's controller 876 and the multiplexer 886 anddemultiplexer 890 disconnect the core's terminals from inputting oroutputting functional signals to neighboring integrated circuitcircuitry. In this mode the core is quiet and its I/O is disabled fromdisturbing testing being performed on the non-core circuitry.

When the core is being tested, but the non-core circuitry is not beingtested, the core's controller 976 is enabled by the integrated circuit'scontroller 876. The integrated circuit's controller 876 controls thecore terminal multiplexer 886 and demultiplexer 890 such that the serialdata output from the integrated circuit's scan distributor circuit 800is input to the core's scan distributor circuit 900, and the serial dataoutput from the core's scan collector circuit 944 is input to theintegrated circuit's scan collector circuit 944. Further, the integratedcircuit controller 876 disables the non-core scan paths from shiftingand capturing data and causes the scan distributor 800 and scancollector circuits 844 to operate as test data pipeline registersbetween the integrated circuit pads 802 and 866 and the core's scandistributor 900 and scan collector 944. During test, the core's scandistributor 900 and scan collector 944 circuits are controlled by thecore's controller 976 to operate as described in regard to FIG. 5 or 6.The only difference is that the depth of the scan data input to andoutput from the core's scan distributor 900 and scan collector 944circuits is greater since the data is pipelined though the integratedcircuit's scan distributor 800 and scan collector 844 circuits.

When both the integrated circuit's non-core and core circuitry are beingtested, both the integrated circuit and core controllers 876 and 976 areenabled. Also the core terminal multiplexer 886 and demultiplexer 890are set to input test data to the core's scan distributor 900 from theintegrated circuit's scan distributor 800, and to output test data fromthe core's scan collector 944 to the integrated circuit's scan collector844. During test, both controllers 876 and 976 are synchronized to theexternal control input from the tester via the peripheral bond pads toallow stimulus data to be scanned into both the integrated circuit andcore scan distributor circuits while response data is scanned out fromboth the integrated circuit and core scan collector circuits.

The test operation of the integrated circuit and core scan distributorand scan collector circuits is identical to that previously described inregard to FIG. 5 or 6. Again, the only difference is that the depth ofthe scan data input and scan data output is greater since the integratedcircuit and core scan distributor and scan collector circuits areserially connected. The advantage of testing both the integratedcircuit's non-core and core circuitry at the same time is that itreduces the test time of the integrated circuit.

These three modes of testing can be setup by scanning the integratedcircuit and core controllers. Referring to FIG. 8, the integratedcircuit controller is connected to integrated circuit pads for input andoutput and the core controller is connected to the integrated circuitcontroller for input and output. A tester that is connected to theintegrated circuit controller input/output bond pads 706 can scan thecontrollers to set up the type of test to be performed. After setting upthe test type, the tester can input control on input pads to cause thecontrollers to operate according to the way the controllers have beenset up. While the integrated circuit 700 has one core, other integratedcircuits may contain multiple cores. Multiple cores can be tested eitherindividually or in combination with other cores and non-core circuits.

In FIG. 9, integrated circuit 1000 contains functional circuitry 1002,which contains first core circuitry 1004. First core circuitry 1004contains second core circuitry 1006. This hierarchical embedding of corecircuitry or cores within cores creates a very difficult testingsituation. The present invention however renders such nesting of corestestable regardless of how deeply embedded they might be within anintegrated circuit.

Functional circuitry 1002 is associated with bond pads 1008. First corecircuitry is associated with terminals 1010. Second core circuitry isassociated with terminals 1012.

In FIG. 10, the scan distributor and scan collector architecture isshown hierarchically extending from the integrated circuit level to thefirst core level, and from the first core level into the second corelevel. Integrated circuit 1000 comprises functional scan test circuits1014 associated with functional circuitry 1002, first scan test circuits1016 associated with first core circuits 1004 and second scan testcircuits 1018 associated with second core circuits 1006.

In accordance with the circuits depicted in FIGS. 7 and 8, test accessto the second scan test circuits 1018 is achieved through the serialpipelines provided by the first scan test circuits 1016 and functionalscan test circuits 1014. Thus the scan distributor 1020 and scancollector 1022 circuits of second core circuits 1006 is achieved via theserial pipelines provided by the scan distributor and scan collectorcircuits 1024 and 1026 of first scan test circuits 1016 and the scandistributor and scan collector circuits 1028 and 1030 of the functionalscan test circuits 1014.

Also as described in regard to FIG. 8, all the functional circuits 1002,first core circuits 1004 and second core circuits 1006 can be testedtogether, in selected combinations, or individually. When testing all ofthe integrated circuit's circuitry together, the scan distributor andscan collector circuits and controllers are set up to allow the testerto input deep stimulus patterns to serially connected scan distributorsand to output deep response patterns from serially connected scancollectors. The test is the same as described in connection with FIG. 8,only the depth of the serial stimulus and response patterns changes asmore scan distributor and scan collector circuits are added to theintegrated circuit's bond pad input and output scan operations.

In FIG. 11, integrated circuit 1100 includes peripheral bond pads 1102,functional circuits 1104 and scan test circuits 1106, 1108, 1110 and1112. Scan test circuits 1106, 1108, 1110 and 1112 are connected inseries to each of bond pads 1114 and 1116.

The scan test circuits 1106, 1108, 1110 and 1112 illustrate a simplifiedview of how scan distributor and scan collector circuits can be usedhierarchically within an integrated circuit to bring about massiveparallel scan testing. Each available pair of integrated circuit bondpads can be viewed as entry and exit points to a hierarchicalarrangement of embedded scan distributor and scan collector circuits.Each scan distributor and scan collector circuit can be serially linkedto the bond pads, either directly, as with the scan distributor and scancollector circuits 1118 and 1120, or via intermediate scan distributorand scan collector circuits, such as scan distributor and scan collectorcircuits 1122 and 1124, or 1126 and 1128.

In FIG. 11, 4 levels of 10 bit scan distributor and scan collectorcircuits are linked to the bond pad pair 1114, 1116 to provide a 40 bitwide test data input and output interface using only two of theintegrated circuit bond pads. Each level could represent thehierarchical position of an embedded core within the integrated circuit.While not shown, all available pad pairs (i.e. pads not used for testcontrol or power/ground) can be similarly connected in a hierarchicalarrangement to 40 bit wide scan distributor and scan collector circuitsinside the integrated circuit. A tester connected to the pad pairs cantransfer test data to the target test circuits residing in theintegrated circuit at each hierarchical circuit level 1-4. The serial toparallel and parallel to serial test data operation of hierarchicallyarranged scan distributors and scan collectors is clear from FIG. 11.

In FIG. 12, integrated circuit 1200 includes scan test circuits 1202connected to bond pads 1204 and 1206. Controller 1208 connects to bondpads 1210 and 1212 and scan test circuits 1202. Integrated circuit 1200also includes core circuits 1214 that include scan test circuits 1216and core circuits 1218 that include scan test circuits 1220. Controller1222 is associated with scan test circuits 1216 and controller 1224 isassociated with scan test circuits 1220.

Multiplexer circuitry 1226 connects scan test circuits 1202 to scan testcircuits 1216 and 1220. A serial output 1228 of scan distributor 1230connects to the multiplexer 1226 and a serial input 1232 of scancollector 1234 connects to multiplexer 1226. Scan test circuits 1216connect to multiplexer 1226 through multiplexer 1236, which alsoreceives a functional input FI, and through demultiplexer 1238, whichalso provides a functional output FO. Scan test circuits 1220 connect tomultiplexer 1226 through multiplexer 1240, which also receives afunctional input FI, and through demultiplexer 1242, which also providesa functional output FO. Controllers 1222 and 1224 also connect tomultiplexer 1226 through respective leads 1244, 1246, 1248 and 1250.

Integrated circuit 1200 provides an alternate configuration for usingscan distributor and scan collector circuits whereby cores 1214 and 1218are individually selected and connected to the integrated circuit's scandistributor and scan collector circuitry and controller for testing.This selection is achieved by placing multiplexer circuitry 1226 betweenthe integrated circuit's scan distributor 1230, scan collector 1234, andcontroller 1208 circuitry, and the cores. Thus the cores 1214 and 1218can be individually connected to the serial data input and output of theintegrated circuit's scan distributor and scan collector circuitry andto the integrated circuit's controller. The integrated circuit'scontroller supplies the control input to the multiplexer circuitry forselecting a core for testing. Once a core is selected and connected tothe integrated circuit's scan distributor and scan collector circuitry,the core is tested as previously described.

It is important to note that when the integrated circuits 446, 700,1000, 1100 or 1200 evolve into a core for use inside another integratedcircuit, their hierarchical scan distributor and scan collector testarchitectures are reusable inside that integrated circuit. The abilityto reuse the test architecture, as well as the test patterns developedfor the architecture, is an important feature of the present invention.This feature prevents having to spend design resources and timeredesigning the core's test architecture each time the core is usedinside a new integrated circuit. A core's scan distributor and scancollector test architecture can be viewed as plug and play as far as itsreuse within an integrated circuit.

In FIG. 13, integrated circuit 1300 contains non-core circuitry 1301,core 1 1302 and core 2 1304 that contain the disclosed scan distributorand scan collector test architecture. Integrated circuit 1300 has bondpads 1306, core 1 1302 has terminals 1308 and core 2 1304 has terminals1310. If each of the cores have a number of terminals that consume mostof the pads on the integrated circuit, they will have to be individuallyselected and tested using the multiplexing approach described in regardto FIG. 12. However, if the cores have a small number of terminalsrelative to the number of integrated circuit pads then parallel orsimultaneous testing of the cores is possible as described in FIG. 14below.

In FIG. 14, non-core circuitry 1301, core 1 1302, and core 2 1304 of theintegrated circuit 1300 of FIG. 13 each contain integrated circuit padconnections to their scan distributor and scan collector architecturesfor parallel testing. This is possible because the number of terminalsrequired to gain access to the scan distributor and scan collectorarchitectures associated with the non-core circuitry, core 1, and core 2is less than or equal to the number of available integrated circuitpads. The test terminals 1402, 1404 for the scan distributor and scancollector architecture for the non-core circuits, as well as the testterminals 1406, 1408 and 1410, 1412 for the scan distributor and scancollector architecture of core 1 and core 2 can all be coupled tointegrated circuit pads of integrated circuit 1300.

For simplification only one pair of scan distributor and scan collectorcircuits are shown in the non-core, core 1 and core 2 examples of FIG.14. However, each example may contain a plurality of scan distributorand scan collector circuit pairs coupling a plurality of grouped scanpaths. Also in FIG. 14 it is seen that each controller within each scandistributor and scan collector architecture is shown connected toseparate integrated circuit pads. Having separate pads coupled to eacharchitecture's scan distributor, scan collector, and controller allowseach architecture to be operated independently. For example, testing ofthe non-core circuitry, core 1, and core 2 could occur in response to adifferent control and data communication at the integrated circuit padscoupled to the respective architectures. Thus testing could occur atdifferent times, have different durations, and/or use different clockrates. The cores 1 and 2 of FIG. 14 may contain embedded cores as shownin FIGS. 9 and 10, each embedded core containing scan distributor andscan distributor architectures and being testable as previouslydescribed.

Controller Description

In FIG. 15A a controller 1500 is an example of the controller used inthe disclosed scan distributor and scan collector architecture. Thecontroller 1500 consists of a test control register 1502, a test controlstate machine 1504, and a multiplexer 1506. The state machine 1504 hasinputs for receiving a test protocol input (TPI), a test clock input(TCI), a test enable input (TEI), and control input from the testcontrol register. The TPI, TCI, and TEI signals are input to thecontroller either by integrated circuit pads, or core terminals, as seenin FIG. 8.

The state machine 1504 has outputs for providing a shift distributor andcollector output (SHDC), a capture collector output (CPC), a shiftparallel scan path output (SHPSP), and a capture parallel scan pathoutput (CPPSP). The SHDC, CPC, SHPSP, and CPPSP signals are output fromthe controller to the scan distributor, scan collector, and scan pathcircuits, as shown in FIG. 8, and are used to control the scandistributor, scan collector, and scan path circuits during test.Additional signals may be output from the state machine as required toprovide different types of control during test. The state machine alsohas control outputs which are input to the test control register.

The test control register 1502 has an input for receiving a serial datainput (SDI) and inputs for receiving control from the state machine. TheSDI signal is input to the controller either by an integrated circuitpad or core terminal, as seen in FIG. 8. The test control register hasan output for providing a serial data output 1 (SDO1), an output forproviding a test enable output (TEO) to a connected lower levelcontroller, and a control bus output that provides control to the statemachine and multiplexer within the controller, and to the scandistributor, scan collector, and scan path circuits of the testarchitecture, including test multiplexers and demultiplexers shown inFIGS. 8 and 12, external of the controller. The multiplexer inputscontrol and SDO1 from the test control register, and a serial data input1 (SDI1). The multiplexer outputs a serial data output (SDO). The SDOsignal is output from the controller either by an integrated circuit pador core terminal, as seen in FIG. 8.

The state machine responds to the TPI, TCI and TEI inputs to: (1)control the operation of the test control register via the controloutput from the state machine, and (2) control the operation of theexternal scan distributor, scan collector, and scan path circuits viathe SHDC, CPC, SHPSP, and CPPSP outputs from the state machine. Thecontrol input to the state machine from the test control register isused to program the way the scan distributor, scan collector, and scanpath circuits are controlled using the SHDC, CPC, SHPSP, and CPPSPsignals. Also, the programming control input to the state machine canalso modify the operation of the SHDC, CPC, SHPSP, and CPPSP signals,and enable additional control output signals to allow other types oftest control sequences to be performed.

State Machine Control of Test Control Register

In FIG. 15B, the test control register 1502 contains a shift register1510 and an update register 1512. The shift and update registers areinitialized by a reset (RST) control output from the state machine. Theshift register shifts data from SDI to SDO1 by a clock (CK) controloutput from the state machine. The update register updates control datafrom the shift register by an update (UPD) control output from the statemachine. The update register is used to prevent the control outputs ofthe test control register from changing as data is shifted through theshift register, and its use as such is well known in the art.

When TEI is low, the state machine is disabled to a known state andoutputs a low on RST to initialize the shift and update registers of thetest control register. When initialized, the test control registeroutputs control to the multiplexer to connect SDO1 to SDO. Also,following initialization, the test control register outputs control tothe state machine to: (1) establish an initial operation mode for thestate machine's SHDC, CPC, SHPSP, and CPPSP outputs, (2) outputs controlto the scan distributor, scan collector, and scan path circuits externalof the controller to enable normal operation of the integrated circuitor core in which the controller resides, and (3) outputs a low on TEO tosimilarly disable and initialize any connected lower level controller.

When TEI is high, the state machine is enabled to respond to the TCI andTPI inputs to scan data through the test control register from SDI toSDO, and to update and output control data from the test controlregister. It is important to note that when the state machine is firstenabled to scan data through the test control register, the scan pathonly includes the test control register between the SDI input and SDOoutput. The control data updated from the test control registerfollowing a scan operation may include control to condition themultiplexer and the TEO output to allow a scan path connected betweenthe SDO1 and SDI1 signals to be added to the test control register scanpath so that it may be included in subsequent test control register scanoperations. A scan path existing between SDO1 and SDI1 that has beenadded to the test control register scan path, may be deleted from beingscanned by conditioning the multiplexer and TEO output to disallow scanoperations through the scan path between SDO1 and SDI1. U.S. Pat. No.4,872,169 by Whetsel, entitled Hierarchical Scan Selection, describes amethod of adjusting scan path lengths.

State Machine Control of Scan Distributor, Scan Collector, and Scan PathCircuits

In addition to responding to TPI and TCI input to operate test controlregister scan operations, the state machine responds to TPI and TCIinput to operate the SHDC, CPC, SHPSP, and CPPSP outputs to the scandistributor, scan collector, and scan path circuits. Prior to operatingthe SHDC, CPC, SHPSP, and CPPSP outputs, a scan operation to the testcontrol register is performed. This scan operation establishes controlinput to the state machine to program the SHDC, CPC, SHPSP, and CPPSPoutputs to operate in modes to support the types of testing previouslydescribed in regard to the non-hierarchical scan distributor and scancollector architecture of FIG. 4 and the hierarchical scan distributorand scan collector architecture of FIG. 8. This scan operation alsoestablishes the type of test mode control which is output from thecontroller and input to the scan distributor, scan collector, scan path,and other associated test circuits, such as the multiplexer anddemultiplexer circuits of FIGS. 8 and 12.

If a non-hierarchical test operation is to be performed, i.e. only asingle controller and its associated scan distributor and scan collectorcircuits are being setup for testing (FIG. 4), a single test controlregister scan operation is all that is required prior to using the statemachine to operate the SHDC, CPC, SHPSP, and CPPSP outputs. However, ifa hierarchical test operation is to be performed, i.e. multiple levelsof controllers and their associated scan distributor and scan collectorcircuits are being setup for testing (FIG. 8), multiple test controlregister scan operations are required, prior to using the state machineto operate the SHDC, CDPC, SHPSP, and CPPSP outputs, to allow the scanpaths of the lower level controllers to be connected to the scan path ofthe highest level controller, as will be described later in regard toFIGS. 17, 18, and 19.

In a non-hierarchical test operation, for example as described in FIG.4, the state machine receives control from TPI and TCI to scan the testcontrol register to setup the test to be performed. Following this scanoperation, the state machine receives further control from TPI and TCIto operate the SHDC, CPC, SHPSP, and CPPSP outputs to control the scandistributor, scan collector, and scan path circuits during the test. Tounderstand better the operation of the state machine, a state diagram isprovided in FIG. 16. This state diagram accompanied by the followingdescription provides a description of how the state machine operates.

In FIG. 16, an example state diagram 1600 of one preferredimplementation of the state machine is shown. This diagram illustrateshow the state machine responds to the TPI and TCI inputs to transitioninto various states that enable scanning of the test control registerand controlling of the scan distributor, scan collector, and scan pathcircuits. The TCI input to the state machine is the clock that times theoperation of the state machine, whereas the TPI input to the statemachine is the input that causes the state machine to transition betweenits states.

Whenever the TEI input is low, the state machine goes to and remains inthe reset (RESET) state 1602 and will not respond to the TPI input. Inthe RESET state, the state machine outputs control to initialize thetest control register as previously described. When the TEI input ishigh, the state machine is enabled to respond to the TPI input. AfterTEI goes high, the state machine remains in the RESET state if TPI ishigh. The state machine transitions to and remains in the idle (IDLE)state 1604 in response to a low on TPI. In the IDLE state, the RSTcontrol input to the test control register (FIG. 15B) is set high toremove the reset condition on the shift and update registers.

In response to a high and low input on TPI, the state machinetransitions to the shift test control register state (SHIFT-TCR) 1606,via the select test control register state (SELECT-TCR) 1608. In theSHIFT-TCR state, the state machine outputs control (CK of FIG. 15B) toshift data through the test control register from SDI to SDO of FIG.15A. The state machine remains in the SHIFT-TCR state for the number ofTCI inputs required to shift data into the test control register. Whenthe shift operation is complete, a high on TPI transitions the statemachine into the update test control register state (UPDATE-TCR) 1610,where the state machine outputs control (UPD of FIG. 15B) to cause theupdate register to load and output the data shifted into the shiftregister.

From the UPDATE-TCR state 1610, the state machine is designed to eithertransition back to the IDLE state 1604 if TPI if low, or transition tothe select test state (SELECT-TEST) 1612 if TPI is high. This two waynext state decision was designed into the state machine to facilitatethe invention's ability to setup either hierarchical or non-hierarchicaltest architectures. For example, if the test setup is for anon-hierarchical test architecture (i.e. FIG. 4), the next state fromUPDATE-TCR is preferably the SELECT-TEST state 1612 to allow the statemachine to immediately start outputting SHDC, CPC, SHPSP, and CPPSPcontrol to the scan distributor, scan collector, and scan path circuits.However, if the test architecture is hierarchical (i.e. FIG. 8), thenext state from UPDATE-TCR will preferably be the IDLE state 1604 toallow transitioning back into the SHIFT-TCR state to scan additionalsetup control data into a lower level controller that has been enabled,via TEO, and whose test control register has been inserted into the testcontrol register scan path of the higher level controller, via SDO1 andSDI1.

When all setup scan operations are completed, the state machine respondsto TPI to transition into the SELECT-TEST state 1612. In the SELECT-TESTstate a decision can be made that will start the test by enabling theSHDC, CPC, SHPSP, and CPPSP outputs, or not start the test and return tothe RESET state. Assuming it is desired to start the test, the statemachine will respond to TPI to transition from SELECT-TEST to the CPCstate 1614. In the CPC state, the state machine outputs CPC control toenable the scan collectors to capture the serial data output from thescan paths. After the data is captured, the state machine responds toTPI to transition into the SHDC state 1616 where the state machineoutputs SHDC control to enable data to be shifted into the scandistributors and shifted out of the scan collectors.

After remaining in the SHDC state long enough to fill the scandistributors and empty the scan collectors, the state machine respondsto TPI to transition into the SHPSP state 1618. In the SHPSP state, thestate machine outputs SHPSP control to enable the scan paths to shift indata from the scan distributors. If the scan paths have not been filledwith data from scan distributors, the state machine will be controlledby TPI to transition from the SHPSP state to the CPC state 1614. If thescan paths have been filled with data from the scan distributors, thestate machine will be controlled by TPI to transition from the SHPSPstate into the CPPSP state 1620. In the CPPSP state, the state machineoutputs CPPSP control to enable the scan paths to capture data fromcombinational logic being tested. If the test is not complete, the statemachine will respond to TPI to transition from the CPPSP state to theCPC state and repeat the above test control sequence. I—the test iscomplete, the state machine can respond to TPI to transition from theCPPSP state directly to the IDLE state 1604.

As seen in FIG. 16, the state machine 1504 may also complete a test bytransitioning into the IDLE state from the CPC state 1614. At the end ofa test, the state machine responds to TPI to transition from the IDLEstate to the RESET state. Alternately, the state machine may enter theRESET state from any state in response to a low on TEI.

The state machine state diagram of FIG. 16 closely mirrors the moregeneral descriptive state diagram previously shown and described inregard to FIG. 6. For example, state 501 of FIG. 6 relates to thestarting of the test, which in FIG. 16 relates to the TEI signal goinghigh. State 502 of FIG. 6 relates to the configuring of a test, which inFIG. 16 relates to the setup scan operation performed by transitionsthrough the SHIFT-TCR and UPDATE-TCR states 1608 and 1610. State 503 ofFIG. 6 relates to the capturing of data outputs from scan paths intoscan collector, which in FIG. 16 relates to the CPC state 1614. State504 of FIG. 6 relates to the filling and emptying of the scandistributors and scan collectors, which in FIG. 16 relates to the SHDCstate 1616.

State 605 of FIG. 6 relates to the inputting of data from the scandistributors to the scan paths, which in FIG. 16 relates to the SHPSPstate 1618. State 508 of FIG. 6 relates to the capturing of data by thescan paths, which in FIG. 16 relates to the CPPSP state 1620. State 509of FIG. 6 relates to exiting the test mode and returning the circuit(integrated circuit or core) back to the normal mode of operation, whichin FIG. 16 relates to transitioning into the RESET state 1602.

In FIG. 6, the inner loop, comprising state transitions 503, 504, 605,and back to 503, used to capture data into the scan collectors from thescan paths, shift data in and out of the scan distributors and scancollectors, and load data into the scan paths from the scandistributors, relates to the inner loop of FIG. 16 comprising statetransitions CPC 1614, SHDC 1616, SHPSP 1618, and back to CPC 1614. Also,in FIG. 6, the outer loop, comprising state transitions 503, 504, 605,508, and back to 503, used to additionally perform the step of capturingdata from the combinational logic into the scan paths after the scanpaths have been filled with data from the scan distributors as a resultof performing the inner loop multiple times, relates to the outer loopof FIG. 16 comprising state transitions CPC 1614, SHDC 1616, SHPSP 1618,CPPSP 1620 and back to CPC 1614.

In the state machine of FIGS. 15A and 16, it is seen that TPI is asingle signal used for regulating the operation of multiple test controlsignal outputs from the state machine. While multiple control signalscould be directly used, instead of having them generated by a statemachine in response to a single TPI signal, it would increase the numberof test control signal paths required to be routed to the controller.The advantage of having a single signal for regulating the operation ofmultiple test control outputs from a state machine will be seen later inregard to FIGS. 17, 18, and 19 where examples of the connectivitybetween hierarchically arranged controllers are shown.

Also, in the above description of the way the state machine controlsscan distributor, scan collector, and scan path circuits it is importantto note that the control outputs do not necessarily need to control theoperations directly, but rather the control outputs may be used toprovide timing windows within which the stated control operation occurs.For example, when the CPPSP control output is generated in the CPPSPstate, the timing to perform the capturing of data into the scan pathmay come from the CPPSP signal directly or, alternately, the CPPSPsignal may simply provide a timing window in which a different signal isallowed to perform the capture operation.

The different signal may for example be a functional clock signal thatnormally controls the registers of the scan path when they are in normalmode and not configured into test mode as previously described in regardto FIGS. 4 and 5. Similarly, the other control signals, CPC, SHDC, andSHPSP may either directly control their stated operations, or,alternatively, each may provide a timing window in which other signalsmay be allowed to control the stated operations. Also, if other signalsare allowed to perform an operation, the number of times the othersignals are allowed to perform the operation will be controlled by thenumber of TCI clocks consumed by the state machine during that timingwindow. For example, the state machine only remains in the SHPSP statefor a single TCI clock period. If the SHPSP control signal enablesanother signal to shift the scan paths during the SHPSP state, thenumber of shifts will be limited to one, regardless of whether the othersignal has a frequency much higher than the frequency of the TCI signal.

Hierarchical Controller Arrangements and Operation

In FIG. 17, multiple controllers 1702, 1704, and 1706 are be connectedin a hierarchy. FIG. 17 relates to previous FIGS. 8 and 10 that depictedembedded cores, each having scan distributor and scan collectorarchitectures, connected to form deep scan distributor and scancollector test channels accessible from the integrated circuits pads. Asmentioned in regard to FIGS. 8 and 10, the integrated circuit'scontroller has authority over lower level controllers to allow theintegrated circuit controller to establish test modes in lower levercontrollers, via the test control register, and to synchronize the testoperations of lower level controllers to the integrated circuit levelcontroller. As previously mentioned, each of the embedded cores may havebeen an integrated circuit prior to being utilized as an embedded core.Each core therefore has the same controller inputs and outputs as wouldan integrated circuit controller, i.e. TPI, TCI, TEI, SDI, SDO, SDO1,TEO, and SDI1. Even if the embedded core were not previously integratedcircuits, they would preferably be designed with these same controllerinputs and outputs to allow hierarchically connecting the cores togetheras described below.

FIG. 15A has provided a detail view and description of the controller.FIG. 17 illustrates how the hierarchical interconnect structure betweenan integrated circuit controller 1702, a core 1 controller 1704 embeddedwithin the integrated circuit, and a core 2 controller 1706 embeddedwithin core 1 is accomplished. The integrated circuit controller 1702 isconnected to the integrated circuit pads via the previously describedTPI, TCI, TEI, SDI, and SDO signals. The integrated circuit controller'sSDO1 output is connected to the SDI input of the core 1 controller 1704.The integrated circuit controller's SDI1 input is connected to the SDOoutput of the core 1 controller 1704. The integrated circuitcontroller's TEO output is connected to the TEI input of the core 1controller 1704. Core 1 controller's SDO1 output is connected to the SDIinput of the core 2 controller 1706. Core 1 controller's SDI1 input isconnected to the SDO output of the core 2 controller 1706. Core 1controller's TEO output is connected to the TEI input of the core 2controller 1706. The TPI and TCI inputs to both core 1 and core 2controllers are directly connected to the integrated circuit's TPI andTCI pads, as is the TPI and TCI inputs to the integrated circuitcontroller. This hierarchical interconnect structure would continue ifadditional embedded cores were present in core 2.

Based on the hierarchical interconnect structure description givenabove, the steps of hierarchically accessing the controllers within theinterconnect structure will now be described. Initially, all controllerswill be reset by the TEI pad input being low. From the controllerdescription of FIG. 15A, if the TEI input is low, the TEO output will below. Therefore, all controllers will be reset by a low on the TEI pad,due to the TEO and TEI connections between the controllers. If TEI isset high, a first scan operation of the integrated circuit controller'stest control register can be performed. This first scan operation setsthe TEI input to the core 1 controller 1704 high, and also selects core1 to be inserted into the integrated circuit controller's scan path, viaSDO1 and SDI1. A second scan operation is performed which scans datathrough both the integrated circuit and core 1 test control registers.This second scan operation sets the TEI input to the core 2 controller1706 high, and also selects core 2 to be inserted into the core 1controller's scan path, via SDO1 and SDI1. A third scan operation cannow be performed to load control data into all test control registers ofthe integrated circuit, core 1, and core 2 controllers to begin a test.

In this description, multiple test control register scan operations havebeen used to enable multiple embedded controllers to be added to thescan path of the integrated circuit controller. This multiple scanoperation is facilitated by the design of the state diagram of FIG. 16,which provides a loop between the IDLE, SELECT-TCR, SHIFT-TCR,UPDATE-TCR, and IDLE states 1604, 1606, 1608, 1610, and 1604. In thisloop, the IDLE state serves as a synchronization state for adding testcontrol registers of lower level controllers to the test controlregisters of higher level controllers. For example, when the TEO outputfrom a higher level controller is input to the TEI input of a lowerlevel controller during the UPDATE-TCR state, the lower level controlleris enabled to follow the TPI input. Thus, as the enabling higher levelcontroller transitions to IDLE from UPDATE-TCR in response to a low onTPI, the enabled lower level controller transitions to IDLE from RESET,also in response to the low on TPI. As a result, synchronization occursbetween the enabling and enabled controllers by having bothtransitioning to the IDLE state, as shown in the state diagram of FIG.16.

In FIG. 17, the TPI and TCI pad signals are bussed directly to eachcontroller 1702, 1704, and 1706. This allows the timing of eachcontroller to be better maintained during scan and test operations,regardless of how many controllers are hierarchically connected. If forexample, the TPI and TCI signals were routed through each controllerprior to being input to a lower level controller, instead of beingdirectly input to each controller from the integrated circuit pads,delays would accumulate in the TPI and TCI signal paths as morecontrollers are hierarchically connected. Eventually, the accumulateddelay would reach a point where the timing of scan and test operationsof lower level controllers would be degraded and the controllers wouldno longer be synchronized to the TPI and TCI pad signals. This wouldcause the test hierarchy to support only a limited number of connectedcontrollers. However, by keeping the TPI and TCI pad signals directlybussed to all controllers, and sufficiently buffered to drive allcontrollers, the test hierarchy would not have the stated controllerconnection limit.

While buffer circuitry is not shown in FIG. 17 and other figures,external signals input to the integrated circuit pads will besufficiently buffered or otherwise amplified to allow them to drive theinternal circuits they are connected to. U.S. Pat. No. 5,056,093 byWhetsel, column 20, lines 31-46, describes the advantage of directlybussing control signals.

In FIG. 17, an advantage in wire routing in the integrated circuitresults from using a single TPI signal to each controller to generate aplurality of control outputs used to operate the scan distributor, scancollector, and scan path circuits. For example, if the control signalsthat operate the scan distributor, scan collector, and scan pathcircuits were not supplied by the state machine, but rather weresupplied from integrated circuit pads and gated by control output fromthe test control register to all scan distributor, scan collector, andscan path circuits, the test control wire routing overhead in theintegrated circuit would increase significantly. Furthermore, it iseasier to design and route a single signal path for minimum signaldegradation and skew than it is to design and route multiple signalpaths for minimum signal degradation and skew. Also, it is usuallypreferred to keep the number of integrated circuit pads dedicated fortest to a minimum number, which the single TPI signal allows.

In FIG. 18, another controller connection scheme is shown. Integratedcircuit 1800 provides an integrated circuit controller 1802 connected toa selected one of a plurality of controllers 1804, 1806 via multiplexercircuitry 1808. This connection scheme was previously described inregard to FIG. 12, and is used whenever the number of core terminalsused for testing consume most of the available integrated circuit pads,such that no other core can be tested simultaneously due to lack ofavailable pads. To select one of the cores 1804, 1806, the integratedcircuit controller 1802 is scanned a first time to load the test controlregister to output mux control to the multiplexer circuitry and toinsert the SDO1 and SDI1 signals of the multiplexer to the integratedcircuit controller's test control register scan path. In response to themux control output, the multiplexer circuitry; (1) connects the SDO1output from the integrated circuit controller to the SDI input of theselected core controller, (2) connects the SDI1 input of the integratedcircuit controller to the SDO output of the selected core controller,and (3) connects the TEO output of the integrated circuit controller tothe TEI input of the selected core controller. The multiplexer circuitryis designed to drive the TEI inputs of non-selected cores low, so thatthey are held in a reset state when they are not selected by theintegrated circuit controller 1802.

With this connection formed between the integrated circuit controller1802 and the core controller, a second scan operation is performed whichloads test control data into the test control registers of theintegrated circuit and core controllers, to establish the test mode tobe used. Following the second scan operation, the test can begin byinputting TPI control to the integrated circuit and core state machinesto generate the control outputs to operate the scan distributor and scancollector architectures of the integrated circuit and core. When testingis complete, a third scan operation is used to deselect the corecontroller from the integrated circuit controller. If another core needsto be tested, the above sequence can be repeated to select, setup, andtest the other core. If no other core needs to be tested, the TEI signalcan be taken low to reset and disable all the controllers within theintegrated circuit 1800, and the multiplexer circuitry 1808.

In FIG. 18, the TPI and TCI signals are bussed directly from theintegrated circuit pads to the controllers to provide the timing andsignal integrity advantage previously mentioned in regard to FIG. 17.While the TPI and TCI signals could be connected to the selected corevia the multiplexer circuitry 1808, as shown in FIG. 12, a directlybussed connection is preferred to avoid the delay introduced by themultiplexer circuitry. If the selected core contains further embeddedcores, those cores can be selected, setup, and tested using thehierarchical connection approach described in regard to FIG. 17.

The structures depicted in FIG. 19 relates to the structures depicted inprevious FIG. 14 where multiple cores and non-core circuits weredescribed being directly connected to integrated circuit pads and testedin parallel. The difference between the structures of FIGS. 14 and 19 isthat in FIG. 14 each circuit's controller was connected to separateintegrated circuit pads to allow each controller to be independentlycontrollable, whereas in FIG. 19, all controllers 1902, 1904, and 1906are connected in the hierarchical fashion described in regard to FIG. 17to allow one set of integrated circuit pads to control all circuitcontrollers. The process for setting up the hierarchically arrangedcontrollers is the same as described in regard to FIG. 17.

A difference between FIGS. 17 and 19 is that in FIG. 17 the test datainput to and output from each circuit passes through a serial pipelineconnection formed via the circuit's scan distributor and scan collectorcircuits, as seen in FIG. 10. In FIG. 19 the test data input to andoutput from of each circuit's scan distributor and scan collectorcircuits is provided by direct connection to integrated circuit pads. Ifthe cores of FIG. 19 contain embedded cores, hierarchical testing asdescribed in regard to FIGS. 10 and 17 can be performed. During scan andtest operations, all controllers operate synchronous to the TPI and TCIpad inputs, which are shown directly connected to each controller.

Pipelining Test Data Through Scan Distributor and Scan CollectorCircuits

It is important to note that when multiple levels of scan distributorand scan collector circuits are connected to form deep serial test datainput and output pipelines, as depicted in FIGS. 8, 10 and 11, thecontroller associated with each scan distributor, scan collector, andscan path circuit level can be setup, by scanning of the controller'stest control register of FIG. 15A, to control the operation of the scandistributor, scan collector, and scan path circuits. As mentioned inregard to FIGS. 8, 10, and 11, the controllers at each level can setuptheir scan distributor, scan collector, and scan path circuits fortesting, or the controllers can setup their scan distributor and scancollector circuits as pipeline registers to transfer test data betweenintegrated circuit pads and scan distributor, scan collector, and scanpath circuits that are setup for testing. If scan distributor and scancollector circuits are being used as pipeline registers, the controllerassociated with the scan distributor and scan collector circuits doesnot output the CPC control signal previously described in FIGS. 15A and16. The CPC signal causes the scan collector to capture data from thescan paths. When pipelining data through the scan collector to be outputfrom an integrated circuit pad, the data must not be overwritten, aswould occur if the CPC signal were output. The following example isgiven to illustrate how data pipelining preferably works whenintermediate scan distributor and scan collector circuits, not beingused for testing, exists between a tester and scan distributor, scancollector, and scan path circuits that are being used for test.

In FIG. 11, the level 4 scan distributor, scan collector, and scan pathcircuits have been setup for testing and the scan distributor and scancollector circuits at levels 1-3 have been setup for pipelining databetween a tester contacting the integrated circuit pads and the level 4scan distributor, scan collector, and scan path circuits. The followingsteps are performed during this test.

The first step is to input 40 bits of data into the four seriallyconnected 10-bit scan distributors and output 40 bits of data from thefour serially connected 10-bit scan collectors during the SHDC state(see FIG. 16 for all state references). After this first step, the level4 scan distributor is loaded with the first 10 bit data pattern to beshifted into the level 4 scan paths during the SHPSP state. Alsofollowing this first step, the level 1-3 scan distributors have beenloaded with the next three 10 bit patterns that will eventually beshifted into the level 4 scan distributor and transferred into the level4 scan paths.

The second step is to transfer the 10-bit pattern from the level 4 scandistributor into the scan paths during the SHPSP state, then capture the10-bit data output from the scan paths into the level 4 scan collectorduring the CPC state. Note that since level 1-3 scan collectors havebeen setup to operate as pipeline registers, their controllers do notoutput the CPC control during the CPC state. As previously mentioned,outputting CPC control to level 1-3 scan collectors would overwrite databeing pipelined to the tester from the level 4 scan collector circuit.

The third step is to input 10 bits of data into the four seriallyconnected scan distributors, and output 10 bits of data from theserially connected scan collector circuits in the SHDC state. Followingthis step, the level 1 scan distributor contains a new 10 bit datapattern from the tester, the level 2 scan distributor contains the 10bit data pattern previously in the level 1 scan distributor, the level 3scan distributor contains the 10 bit data pattern previously in thelevel 2 scan distributor, and the level 4 scan distributor contains the10 bit data pattern previously in the level 3 scan distributor. Alsofollowing this step, the tester contains the 10 bit data patternpreviously in the level 1 scan collector, the level 1 scan collectorcontains the 10 bit data pattern previously in the level 2 scancollector, the level 2 scan collector contains the 10 bit data patternpreviously in the level 3 scan collector, and the level 3 scan collectorcontains the 10 bit data pattern previously in the level 4 scancollector.

Following the third step, the second step is repeated, then the thirdstep is repeated. This sequence of repeatedly doing the second and thirdsteps continues until the level 4 scan paths are filled with data, atwhich time a fourth step of capturing data into the level 4 scan pathduring the CPPSP state occurs. Following the fourth step, the sequenceof repeatedly doing the second and third steps continues, periodicallyperforming the fourth step as the level 4 scan paths fill with data.Eventually the test is complete and the controllers are transitionedback into their RESET states. Note that the last scan distributor andscan collector shift operation in the third step needs to be ofsufficient duration to allow the last data captured into the level 4scan collector from the scan paths to be communicated to the tester.

What is important understand in the above example is the ability ofnon-testing scan distributor and scan collector circuits, locatedbetween a tester and testing scan distributor and scan collectorcircuits, to serve as pipeline registers which provide temporary storagefor data being transferred between the tester and testing scandistributor and scan collector circuits. For example, in step one abovethe tester had to initially transfer 40 bits of data into and out of thelevel 1-4 scan distributor and scan collector circuits, to get the first10 bit data input and output pattern to and from the level 4 scandistributor and scan collector circuits. If the level 1-3 scandistributor and scan collector circuits could not be controlled tooperate in the pipeline mode, this 40 bit transfer would have to occureach time a new 10 bit data input and output pattern is required to betransferred between the tester and level 4 scan distributor and scancollector circuits. In this example, this would extend the test time byapproximately a factor of 4. However, since the level 1-3 scandistributor and scan collector circuits can be controlled to operate ina pipeline mode during steps 2 and 3, the tester only has to communicate10 bits of data during each SHDC state. Again, the key to this is theability to scan the test control registers of the level 1-3 controllersto cause their state machines to not output the CPC control signalduring the CPC state.

While this example uses a 40 bit deep pipeline, other examples may haveshorter or longer pipelines, depending upon the depth of the scandistributor and scan collector test hierarchy being traversed. Using thepipelining approach described above advantageously cancels out the depthof any scan distributor and scan collector test hierarchy, and enablesthe tester to be viewed as being directly connected to the testing scandistributor and scan collector circuitry, regardless of the pipeline bitlength between the tester and testing scan distributor and scancollector circuitry. Being able to test a circuit, a core for example,embedded N levels deep in approximately the same amount of time as itwould take to test the same circuit in a non-embedded or direct fashionis a very important aspect of the present invention.

Another important aspect of the pipelining capability is the fact thatthe test patterns used to test the embedded circuit in the exampleabove, are the same test patterns used to test the same circuit if itwere not embedded. The only difference in the test patterns is that theymust be temporarily registered along the additional non-testing scandistributor and scan collector circuits prior to being input and outputto the target circuit being tested via the testing scan distributor andscan collector circuits.

Test Pattern Formatting

In conventional scan path design, test patterns are formatted to allow atester to scan directly into and out of a scan path, as described inregard to FIG. 2. However, using the present invention the test patternsneed to be formatted differently to allow navigating the test patternsthrough scan distributor and scan collector circuits located between thetester and scan paths.

In FIG. 20A, system 2000 provides an integrated circuit 2002, a testerdriver 2004 and a tester receiver 2006. Integrated circuit 2002 containsa simplified example of a pair of scan paths, scan path 1 2008 and scanpath 2 2010, interfaced to the tester driver and receiver channel by 2bit deep scan distributor and scan collector circuits 2012, 2014. Whilethe ideal case would be for all scan paths to be of the same bit length,that may not always be the case. To illustrate how scans to differentlength scan paths are performed using the present invention, scan path 1is shown being 5 bits long and scan path 2 is shown being 4 bits long.The tester driver 2004 comprises a shift register means 2016 fortransmitting data to the scan distributor and scan paths, a memory means2018 for storing data transmitted by the shift register, and a controlmeans 2020 for regulating the operation of the shift register andmemory. The tester receiver 2006 comprises a shift register means 2022for receiving data from the scan collector and scan paths, a memorymeans 2024 for storing data received by the shift register, and acontrol means 2026 for regulating the operation of the shift registerand memory.

To support the scan distributor circuit interface between the tester andscan paths, the data stored in the driver memory is formatted into leftand right columns. In the driver memory 2018, the data shown in the leftcolumn (D1-D5) is the data that would normally be shifted into scan path1, if scan path 1 was conventionally connected directly to a testerdriver. Similarly, the data (D1-D4) in the right column of the drivermemory is the data that would normally be shifted into scan path 2, ifscan path 2 was conventionally connected directly to another driver.However, since scan path 1 and scan path 2 are interfaced to the sametester driver, via scan distributor, the data output to scan path 1 andscan path 2 is formatted into left and right columns as shown.

To support the scan collector circuit interface between the tester andscan paths, the data stored in the receiver memory is formatted intoleft and right columns. In the receiver memory 2024, the data shown inthe right column (D1-D5) is that data that would normally be shifted outof scan path 1, if scan path 1 was conventionally connected directly toa tester receiver. Likewise, the data (D1-D4) in the left column of thereceiver memory is the data that would normally be shifted out of scanpath 2, if scan path 2 was conventionally connected directly to anothertester receiver. However, since scan path 1 and scan path 2 areinterfaced to the same tester receiver, via scan collector, the datainput from scan path 1 and scan path 2 is formatted into left and rightcolumns as shown.

In operation, the driver's controller loads the shift register with thefirst row of left and right column data, i.e. D5 and X, from the drivermemory. The controller then causes the shift register to shift the leftand right column data (D5 and X) into the scan distributor, such that Xinputs to scan path 2 and D5 inputs to scan path 1. The scan paths arethen shifted to input the D5 and X. Next, the second row of left andright column data in the memory, D4 and D4, is similarly loaded into theshift register, shifted into the scan distributor, then shifted into thescan paths. This process repeats with subsequent rows of left and rightcolumn data until the scan paths have been filled, such that scan path 1contains D1-D5 and scan path 2 contains D1-D4. The X bit in the firstrow of data shifted out is a placeholder that serves to pad or balancethe data being shifted into the uneven length scan paths. If the scanpaths had even lengths, the X would not be required.

Simultaneous with the above described driver operation, the receiver'scontroller operates the receiver shift register to shift in data fromthe scan collector, as scan distributor is being shifted, such that datathat has been captured into scan collector from scan path 1 is storedinto the right column of the receiver memory and data that has beencaptured into scan collector from scan path 2 is stored into the leftcolumn of the receiver memory. At the end of the above described driveroutput operation, where its memory has output rows of left and rightcolumn data to the scan distributor, the receiver memory will havefilled with rows of left and right column data from the scan collector.The left column of the receiver memory is filled with scan path 2 data(D1-D4), and the right column is filled with scan path 1 data (D1-D5).Again due to the uneven length between scan path 1 and scan path 2, thelast data input to the left column of the receiver memory from scan path2 will be X. With even length scan paths, no X's would be input to thereceiver memory.

After the above described shift in and out sequence occurs, the nextformatted data to be shifted out to the scan paths is available in thedriver memory, and new locations of receiver memory are available forstoring data shifted out of the scan paths during the next sequence.

In FIG. 20B, system 2050 provides an integrated circuit 2052, testerdriver 2054 and tester receiver 2056. This embodiment illustratesanother example of data formatting where the tester must communicatewith scan distributors and scan collectors pairs of uneven length. Scandistributor 2058 and scan collector 2060 pair connect to two scan paths2062 and 2064, as described above. Scan distributor 2066 and scancollector 2068 pair connect to three scan paths 2070, 2072, and 2074,each having different lengths. The basic operation is the same asdescribed in FIG. 20A, with the exception that a third column of datamust be formatted for the driver and receiver memories. This thirdcolumn is used for inputting and outputting data to the third scan path2074 of the scan distributor and scan collector pair 2066, 2068. Whilethe scan distributor and scan collector pair 2058, 2060 does not have athird scan path to communicate to, its driver and receiver memories areformatted to include a third column of X's to pad or balance the datainput and output communication of the scan distributor and scancollector pairs 2058, 2060 and 2066, 2068. So, while uneven length scanpaths require padding bits as described in regard to FIG. 20A, unevenlength scan distributor and scan collector pairs require padding columnsas depicted in FIG. 20B. It is important to note that even though thescan distributor and scan collector pair 2058, 2060 is not testing asefficiently as it was in FIG. 20A due to the additional shifts requiredfor the X bits and X columns, it is testing while the scan distributorand scan collector pair 2066, 2068 is testing.

Power Reduction Advantage

During scan testing, conventional scan paths, as described in regard toFIG. 2, shift data in and out at the frequency of the scan clock. Aspreviously described in regard to FIG. 4, a scan path inputs data to andreceives data from combinational logic being tested. Thus, in aconventional scan path, as data shifts through the scan path the inputsto the combinational logic from the scan path may transition at the scanclock frequency. Transitioning the inputs of the combinational logicconsumes power which produces heat in the integrated circuit. The amountof power consumed is related to the frequency of the input transitionsto the combinational logic, which is related to the scan clock frequencyshifting data through the scan path.

In FIG. 21A, integrated circuit 2100 includes a section of a scandistributor 2102 and scan collector 2104 circuit connecting two scanpaths 2106, 2108. The scan paths input data to and receive data fromcombinational logic 2110, via functional input (FI) and functionaloutput (FO) signals. Each scan path comprises a series of connectedconventional scan cells, as shown in FIG. 21B. In the scan paths, thedotted boxes indicate the presence of the scan cell and the connectionof the scan cells to each other, via serial input (SI) and serial output(SO), and to the combinational logic, via FI and FO. The test modeoperation of the FIG. 21B scan cell to capture FI data and shift datafrom SO to SI is well known in the art of scan testing. While only twoscan paths are shown in FIG. 21A, the scan distributor and scancollector circuits may be connected to many additional scan paths, eachscan path being similarly connected to combinational logic via FI andFO.

In FIG. 21A, each scan cell provides outputs to the combinational logic,via FO, and to the next scan cell's SI input, via SO, except for thelast scan cell which outputs to the combinational logic and the scancollector. FO and SO are the same node. There are techniques used toisolate FO and SO during scan so that FO is static while SO outputs.However, these techniques require adding and inserting circuitry, suchas latches or gates, in the FO signal path between the scan cell outputand input to the combinational logic and controlling the added circuitryto update at the end of each scan operation. Examples of such isolationcircuitry is described in IEEE 1149.1 standard. The first scan cell's SIinput is connected only to the scan distributor 2102. Each FO to thecombinational logic is shown fanned out to many combinational logicinputs, which is typical. Capacitor C1 represents the capacitive load ofthe SI input of the scan cell driven by the scan distributor. CapacitorC2 represents the capacitive load of combinational logic inputs drivenby FOs. Capacitor C3 represents the combined capacitive load associatedwith the all gate interconnects within the combinational logic.Capacitance C1 is small compared to capacitances C2 and C3.

If the scan paths 2106, 2108 were connected to integrated circuit padsas conventional scan paths, instead of to scan distributor and scancollector circuits, they would scan data at the scan clock inputfrequency. If the scan clock frequency were 100 MHz, and alternatingdata bits were shifted through the scan path during each scan clockperiod, the FO outputs from the scan paths would transition at 100 MHz.This means that each C2 combinational logic input load would charge anddischarge at that frequency. Also, the capacitance C3 gate interconnectload will charge and discharge in response to the transitions at thecombinational logic inputs. The power consumed during test by thecharging and discharging of capacitances C2 and C3 increases as scanclock frequency increases and decreases as scan clock frequencydecreases.

When using the scan distributor and scan collector circuits 2102, 2104to scan data through the scan paths, the power consumed during test isreduced, compared to the conventional scan description above, since thescan clock frequency of the scan path circuits is reduced. For example,operating 10 bit scan distributors and scan collectors 2102, 2104 usinga 100 Mhz clock and according to the previously described inner loop ofthe controller state diagram of FIG. 16 (i.e. the state transition loopfrom the CPC state to the SHDC state to SHPSP state and back to CPCstate) will result in transitioning through the SHPSP state once everytwelve 100 Mhz clock cycles. Since SHPSP is the state that scans datainto scan paths 2106, 2108 from the scan distributor 2102, the scanpaths are scanned at frequency of 100 Mhz/12 or 8.3 Mhz. Charging anddischarging the capacitances C2 and C3 loads at this slower frequencyreduces the power consumed during test. Operating the scan distributorat 100 MHz will cause the capacitance C1 load it drives to charge anddischarge at 100 MHz, but since capacitance C1 is small compared tocapacitances C2 and C3, the power consumed is negligible. Also, aspreviously described in regard to FIG. 6, the test time is notsignificantly decreased when using the scan distributor and scancollector circuits 2102, 2104 since an amplified number of smallerlength scan paths are capable of being used to transmit test data to andfrom combinational logic being tested.

The following example illustrates the power reduction possible usingscan paths connected to 10 bit scan distributors and scan collectors asshown in FIGS. 4 and 21A, rather than using conventional scan pathsconnected to pads as shown in FIG. 2. The power consumed by C2 and C3 ofcombinational logic 2100 if connected to conventional scan path 1 200 ofFIG. 2 during scan operations can be estimated by; P=CV²F, where C isthe lumped combinational logic C2 and C3 capacitance described in FIG.21A, V is the IC voltage, and F is the frequency of the scan path FOoutputs. The power consumed after modifying scan path 1 of FIG. 2 into agroup of 10 shorter length scan paths of FIGS. 4 and 21A and connectingthem to 10 bit scan distributors and scan collectors, as described inregard to FIG. 3, can be estimated by; P=CV²(F/12), where C is again thelumped combinational logic C2 and C3 capacitance, V is again the ICvoltage, and (F/12) is the scan frequency of the modified scan path FOoutputs (i.e. (F/12) is the frequency of SHPSP state transitions in theinner loop as described above).

From this example it is seen that for a given C, V, and F, the powerconsumed by combinational logic 2110 being scan tested using scan pathsmodified for connection to scan distributor and scan collector circuitsof FIGS. 4 and 21A is approximately 1/12 the power consumed by the samecombinational logic 2110 if it were scan tested using the conventionalscan path arrangement of FIG. 2.

It is important to note that test power consumption decreases further asthe depth of the scan distributor and scan collector increases, sincethe frequency of the SHPSP state in the inner loop of FIG. 16 statediagram decreases. For example, with 40 bit deep scan distributors andscan collectors connected to forty 25 bit scan paths, appropriatelymodified from the FIG. 2 scan path as described in FIG. 3, the power canbe estimated by; P=CV²F/42, where F/42 is the frequency of the scanpaths FO outputs (i.e. the frequency of the SHPSP state of the innerloop of FIG. 16). From this example it is seen that the power consumedby combinational logic 2110 being scan tested using 40 bit scandistributors and collectors and appropriately modified scan paths isapproximately 1/42 the power consumed by the same combinational logic2110 if it were scan tested using the conventional scan path arrangementof FIG. 2.

It is also important to note that as the depth of scan distributors andscan collectors increase, the scan cycle time of scan distributor andscan collector arrangements approach the scan cycle time of conventionalscan path arrangements, as described previously in regard to FIGS. 4 and6 above. Therefore increasing the depth of scan distributors and scancollectors advantageously reduces both IC test power consumption and ICtest time.

In FIG. 22A, arrangement 2200 is used to further reduce the powerconsumed during testing. In the description of FIGS. 21A and 21B thetransitioning of the scan path's FO outputs was described to occur inresponse to a single scan clock used to shift data through the scanpath. Using the same scan clock to shift data through all scan pathscauses simultaneous transitions on the FO outputs of all the scan paths.This causes all the capacitive C2 and C3 loads driven by FO outputs tobe charged or discharged simultaneously, which will consume the mostpower.

As described previously in regard to FIGS. 15A and 16, the SHPSP stateoutputs a SHPSP signal which can either shift the scan paths directly orserve as a timing window to enable another signal to shift the scanpaths. The example in FIG. 22A provides for the SHPSP signal to be usedas a timing window to allow another signal to produce a strobe thatclocks the scan path circuits. The SHPSP and other signal 2202, afunctional clock for example, are input to a synchronizer circuit 2204.The synchronizer is enabled by SHPSP being high to allow one of theclock pulses of the other signal to pass through to the synchronizer'sstrobe output. Note that the design of the synchronizer only allows oneclock pulse to be output on the strobe output 2206 even though thesignal produces multiple clock pulses during the SHPSP timing window(i.e. while SHPSP is high). In other states, such as SHDC, where thestate machine remains for longer than one TCI clock, a new timing windowwill be produced for each TCI clock that occurs during the state.However, as described above, only one strobe output will be producedwithin each new timing window.

If the strobe were directly input to all scan paths, all the scan pathswould shift at the same time. This would produce the simultaneous chargeor discharge situation mentioned above. To prevent this, the strobe isinput to a series of buffers 2208, 2210, 2212, and 2214 connected suchthat the output of the first buffer drives scan path 1 and the input ofthe second buffer, the second buffer drives the input of scan path 2 andthe input of the third buffer, and so on until the last buffer drivesonly the last scan path.

The power reduction made possible by the scan distributor and scancollector architecture alone, or in combination with the synchronizerand delay circuitry described in FIG. 22A, enables more circuits in anIC to be tested in parallel. For example, if an IC contains multiplecircuits to be tested, it is preferable to test all the circuits inparallel to reduce the IC's test time, which reduces wafer and ICmanufacturing cost. However, if each circuit uses conventional scandesign it may not be possible to test all circuits in parallel since thepower consumed by simultaneously testing all circuits may exceed the ICspower handling capacity. Therefore, using conventional scan design, thetest time of an IC may increase since circuits in the IC may need to betested one at a time to limit the test power consumption. However, usingthe scan distributor and scan collector architecture it may be possibleto test all circuits in an IC in parallel and therefore reduce IC testtime, which reduces costs.

FIG. 22B depicts the timing of these series connected signals.

Each scan distributor and scan collector pair could have its ownsynchronizer and clock skewing buffer arrangement 2200, or onesynchronizer and clock skewing buffer arrangement could be used for allscan distributor and scan collector pairs. Alternately, one synchronizercould be used to provide a common strobe signal to multiple clockskewing buffer arrangements. Using this approach, the shifting of datathrough each scan path will be staggered in time. Therefore thetransitions on the FO outputs of each scan path will be staggered intime, as will the charging and discharging of capacitances C2 and C3driven by the FO outputs. Simultaneous power consumption will thereforebe reduced.

While the example circuit of FIG. 22A is shown producing skewed strobeoutputs to reduce the simultaneous power consumed by the scan paths in agiven test timing window, the circuit could also be used in normalfunctional operation to reduce simultaneous power consumed by functionalregisters in a given functional timing window.

Test Controller Programming for Optimized Testing of Particular Circuits

It is important to note that while the scan distributor and scancollector architecture has been shown testing combinational logic, othertypes of circuits can be tested as well, including memories, such asRAMs, and mixed signal circuits, such as digital to analog converters(DAC) and analog to digital converters (ADC). The following examplesillustrate how the testing of other types of circuits is accomplishedusing the scan distributor and scan collector architecture.

Improved Testing of Embedded Memory Cores

In FIG. 23A-1, integrated circuit 2300 includes a RAM memory 2302connected, in test mode, to two scan distributor circuits 2304, 2306 anda scan collector circuit 2308. The scan distributor and scan collectorcircuits are connected, in test mode, to integrated circuit pads or coreterminals 2310, 2312, 2314. One of the scan distributor circuits 2304provides data input (DI) to the RAM and the other scan distributorcircuit 2306 provides address input (AI) to the RAM. The scan collectorcircuit 2308 provides data output (DO) from the RAM.

FIG. 23A-2 shows how the SELECT-TEST portion 2316 of the state diagramof FIG. 16 is programmed to operate when testing the RAM. Theprogramming control of the state machine is input to the state machinefrom the test control register, as mentioned previously in regard toFIG. 15A.

While many types of RAM test sequences can be programmed into the statemachine, this test is programmed to repeat the steps of addressing theRAM, writing data to the addressed location, then reading back the datawritten into the addressed location. At the beginning of the test, thestate machine enters the SHDC state 2318 (from the SELECT-TEST and Readstates) to shift data and address into the scan distributors, and datafrom the scan collector. Next, the state machine enters the Write state2320 to store data shifted into the scan distributor into the RAMlocation addressed by the address shifted into the other scandistributor. Next, the state machine enters the Read state 2322 to readback the data from the addressed location into the scan collector. Thedata read back should equal the data written.

During the Write state the controller outputs control to the RAM towrite data. During the Read state the controller outputs control to theRAM to read data and also outputs control to cause the scan collector tocapture the data being read. This process of shifting the scandistributors and scan collector to input data and address to and outputdata from the RAM, in combination with appropriately controlling the RAMto write and read data, repeats until all RAM locations have beenwritten to and read from. The test can repeat with another set of datato be written and read into each address.

Improved Testing of Embedded Mixed Signal Cores

In FIG. 23B-1, an integrated circuit 2330 includes a digital to analogconverter (DAC) 2332 connected, in test mode, to a scan distributorcircuit 2334 at its digital input and to an integrated circuit pad orcore terminal 2336 at its analog output. The scan distributor circuit2334 is connected, in test mode, to an integrated circuit pad or coreterminal 2338. The scan distributor circuit 2334 provides the digitalinput to the DAC and the analog output provides analog output from theDAC.

FIG. 23B-2 shows how the SELECT-TEST portion 2340 of the state diagramof FIG. 16 is programmed to operate when testing the DAC.

While many types of DAC test sequences can be programmed into the statemachine, this test is programmed to repeat the steps of inputtingdigital data to the DAC, converting the digital data into an analogoutput, and outputting the analog output to a tester for inspection. Atthe beginning of the test, the state machine enters the shiftdistributor state (SHD) 2342 (from the SELECT-TEST state) state to shiftdigital data from an external tester into the scan distributor. Next,the state machine enters the Convert state 2344 to cause the DAC toconvert the digital data from the scan distributor into an analogoutput. The analog output is inspected by an external tester connectedto the analog output pad/terminal. The state machine remains in theConvert state long enough for the conversion to take place and for thetester to inspect the analog output, then enters the SHD state to loadthe next digital input to be converted into analog output and inspected.This process repeats until all digital input codes have been input tothe DAC and converted into analog outputs. The test can repeat with adifferent sequence of digital inputs if desired.

In FIG. 23C-1, an integrated circuit 2350 includes an analog to digitalconverter (ADC) 2352 connected, in test mode, to a scan collectorcircuit 2354 at its digital output and to an integrated circuit pad orcore terminal 2356 at its analog input. The scan collector circuit isconnected, in test mode, to an integrated circuit pad or core terminal2358. The scan collector circuit 2354 provides digital output from theADC and the analog input provides analog input to the ADC.

FIG. 23C-2 shows how the SELECT-TEST portion of the state diagram ofFIG. 16 is programmed to operate when testing the ADC.

While many types of ADC test sequences can be programmed into the statemachine, this test is programmed to repeat the steps of inputting analoginput to the ADC, converting the analog input into a digital output, andoutputting the digital output to a tester for inspection. At thebeginning of the test, an analog input from an external tester is inputto the ADC via a pad/terminal. Next, the state machine enters theConvert state 2360 (from the SELECT-TEST state) to cause the ADC toconvert the analog input into digital output. The state machine remainsin the Convert state long enough for the conversion to take place. Next,the state machine enters the CPC state 2362 to capture the digitaloutput into the scan collector. Next, the state machine enter the shiftcollector (SHC) state 2364 to shift the scan collector to output thedigital output to an external tester. This process repeats until alldigital output codes, representative of the applied analog inputs, havebeen output from the ADC to the tester. The test can repeat with adifferent analog input signal and resulting digital outputs if desired.At the end of this and the other two test examples above, the statemachine returns to either the IDLE or RESET state as shown in FIG. 16.

It is important to note in the above examples, that if the RAM, DAC, orADC is a core embedded deep inside an integrated circuit, the previouslydescribed method of pipelining data, can be used to improve digital testdata bandwidth to and from the circuits. Also note that if pipelining isused, the controllers of the intermediate scan distributor and scancollector circuits, that pipeline the data, must be programmed tooperate according to the state diagrams of FIGS. 23A-1, 23B-1, and 23C-1for synchronous operation. Further, the pipelining controllers ofintermediate scan distributor and scan collector circuits must disablethe capture collector signals during the read state 2322 of 23A-2 andCPC state 2362 of 23C-2 to avoid overwriting data being pipelined, aspreviously mentioned. As mentioned previously in regard to FIGS. 15A,16, and 22A, the control signals output from the controllers may controltesting directly or may operate as timing windows within which anothersignal may be enabled to control testing.

Hierarchical Routing of Analog Test Signals

While not shown in the above examples, multiplexing circuitry isprovided to allow the circuits to be connected to the scan distributor,scan collector, and analog input and output signals while in test mode,and to functional inputs (FI) and outputs (FO) during normal mode,similar to that shown in FIG. 8. It is also important to note that, inthe above examples, the circuits being tested are connected, in thisparticular test mode, directly to the scan distributor and scancollector circuits, and not through scan paths as previously describedin the testing of combinational logic. Also, the internal routing ofanalog inputs and outputs between the external tester contacting theintegrated circuit pad and a terminal to an embedded DAC or ADC shouldbe designed carefully so that the analog signal is not significantlydegraded or otherwise modified.

In FIG. 24, for example, the direct routing scheme described for the TPIand TCI signals in FIG. 17 can be used for routing the analog test inputand output signals between integrated circuit pads 2406, 2408 andterminals 2424, 2426 of embedded mixed signal cores 1, 2, and 3 withinthe integrated circuit 2400. The analog multiplexer and demultiplexercircuitry, such as 2402, 2404, at the analog test input and outputterminals 2424, 2426 of the cores can be controlled by the integratedcircuit's controller to allow either test or functional input andoutput, as described in FIG. 8. The analog multiplexer and demultiplexercircuitry may be designed for bi-directional operation usingtransmission gates, or for unidirectional operation using buffers. Whennot used for outputting analog test signals, the test outputs of thedemultiplexers 2404 are disabled from driving pad 2408. Core 3 2410includes a direct routing scheme that is hierarchical to allow furtherconnection to core 3A 2412 and core 3B 2414 within Core 3. Within Core3, the operation of the analog multiplexers and demultiplexers 2416,2418 of Core 3A and Core 3B are controlled by Core 3's controller, notthe integrated circuit's controller.

Also in FIG. 24, integrated circuit 2400 includes isolation switches 1and 2 (IS1 and IS2) 2420, 2422 on the integrated circuit's analog inputand output pads. In normal mode, the integrated circuit's controllercloses IS1 and IS2, and in test mode, the integrated circuit'scontroller opens IS1 and IS2. Opening IS1 in test mode isolates the pad2406 from functional inputs (FI) it may be connected to in normal mode,which eliminates loading and prevents the analog test inputs fromeffecting the functional inputs (FI) of circuitry connected to the padduring normal integrated circuit operation mode. Opening IS2 in testmode isolates the pad 2408 from functional outputs (FO) it may beconnected to in normal mode, which allows the analog test output from aselected core to drive out on the pad without opposition from functionaloutputs. While not shown, similar isolation switches exist within eachembedded core. The isolation switches of each core are controlled by thecore's controller.

In regard to the testing of digital circuits, similar isolation, to thatmentioned above, is provided for digital test input and output asdescribed in FIG. 14A of U.S. Pat. No. 5,606,566 to Whetsel, the patentmentioned in regard to FIG. 2. According to the present invention asdescribed above for analog test input and output isolation, digital testinput and output isolation at the integrated circuit level is controlledby the integrated circuit's controller while digital test input andoutput isolation at the core level is controlled by the core'scontroller.

Modifying the IEEE 1149.1 TAP for Use in Scan Distributor and ScanCollector Architectures

The description of the scan distributor and scan collector architecturehas shown how it can be used in an integrated circuit and within coresembedded within integrated circuits. Another test architecture that canbe used in integrated circuits and within cores embedded withinintegrated circuits is the IEEE 1149.1 Test Access Port and BoundaryScan Architecture. The following description illustrates how the scandistributor and scan collector architecture and the IEEE 1149.1architecture can be designed to coexist within an integrated circuit orwithin cores embedded within integrated circuits. Of particularimportance is the way the IEEE 1149.1 architecture will be shownmodified or improved to allow it to utilize the same test interface asis used by the scan distributor and scan collector architecture, and touse the same method of hierarchical connectivity used by the scandistributor and scan collector architecture.

In FIG. 25A, a conventional 1149.1 Test Access Port (TAP) 2500 comprisesinputs and output for a test data input (TDI), test data output (TDO),test mode select (TMS), and test clock (TCK). The TAP also comprises aTAP controller state machine 2502, an instruction register 2504, aplurality of data registers 2506, multiplexer 1 (Mux1) 2508, andmultiplexer 2 (Mux2) 2510. The TAP controller is connected to TMS andTCK, and responds to these signals to shift data through either theinstruction register or a selected data register, from TDI to TDO.During instruction register shift operations, the TAP controller causesMux2 to connect the output of the instruction register to TDO. Duringdata register shift operations, the instruction loaded in theinstruction register selects one of the data register outputs to beoutput from Mux1, and the TAP controller controls Mux2 to connect theoutput of Mux1 to TDO. The structure and operation of the TAP, as itwill be referred to hereafter, is widely understood.

In FIG. 25B, a conventional TAP 2530, like the TAP 2500 of FIG. 25A, ismodified to allow it to coexist and operate with the scan distributorand scan collector controller of FIG. 15A. The modifications include:(1) inserting a third multiplexer (Mux3) 2532 between the output of Mux22534 and TDO, which corresponds to the multiplexer in FIG. 15A; (2)providing a TDI1 input to Mux3, which corresponds to SDI1 of FIG. 15A;(3) providing a TDO1 output from Mux2, which corresponds to SDO1 of FIG.15A; (4) providing instruction control to Mux3 to allow an instructionto select TDO1 or TDI1 to be output to TDO, which corresponds with thecontrol output from the test control register to the multiplexer of FIG.15A; (5) providing a port enable input (PEI) signal to the TAPcontroller 2536 to enable or disable the TAP, which corresponds to theTEI signal to the test control state machine of FIG. 15A; and (6)providing a port enable output (PEO) signal from the TAP's instructionregister 2538 to enable lower level TAPs, which corresponds to the TEOsignal from the test control register of FIG. 15A.

With these modifications, the TAP 2530 operates as the conventional TAP2500 when enabled by PEI and while Mux3 is controlled to make aconnection between Mux2 and TDO. When Mux3 is controlled by aninstruction shifted into the instruction register 2538 to insert a scanpath between TDO1 and TDI1 into the TAPs TDI and TDO scan path, the TAP2530 leaves the conventional mode of operation and enters the new modeof operation made possible by the present invention.

It is important to note that control of Mux3 2532 is only possible byperforming an instruction scan operation. Data scan operations throughthe TAP 2530 cannot modify the control of Mux3. This is an advantagesince it allows the scan path length adjustment capability provided byMux3 to take place only in response to instruction scan operations, andnot during data scan operations. Also, while Mux3 is shown existingwithin the TAP 2530, it could exist external of the TAP as well. If itwere external of the TAP, it would still be connected, as shown in FIG.25B, to the instruction register 2538 and TDO1 and TDI1 signals.

U.S. Pat. No. 4,872,169, previously mentioned in regard to FIG. 15A,describes an adjustable length scan path architecture. In this patent,the scan path length is adjustable during each scan operation. The abovementioned method of using Mux3 2532 to adjust the scan path length onlyduring instruction scan operations, and not during data scan operations,is novel over the mentioned patent. Also, the above improvement is novelover conventional TAPs, since conventional TAPs (FIG. 25A) do not have aMux3 to provide the hierarchical capability to link or unlink the TDI toTDO scan path of a lower level TAP to or from the TDI and TDO scan pathof a higher level TAP. Furthermore, conventional TAPs do not provide thecapability of outputting PEO control from a higher level TAP to enableor disable the operation of a lower level TAP, such that when enabledthe TDI to TDO scan path of the lower level TAP is included in the TDIto TDO scan path of the higher level TAP, and when disabled, the TDI toTDO scan path of the lower level TAP is excluded from the TDI to TDOscan path of the higher level TAP.

IEEE TAP Design with Instruction Adjustable Scan Length

It is important to note that while the focus of this description is thedesign of a TAP that can coexist within a scan distributor and scancollector architecture, the way the TAP is modified in regard to FIG.25B to hierarchically insert or delete a lower level TAP scan path intoand from a higher level TAP scan path is important independent of thescan distributor and scan collector architecture. This inventionincludes the modifications of the conventional TAP as depicted in FIG.25B and the above mentioned capability to only adjust the scan pathlength during instruction scan operations.

The ability to enable or disable a TAP using a signal like PEI is known.A known example of how a TAP may be enabled or disabled is described ina paper entitled “An IEEE 1149.1 Based Test Access Architecture forintegrated circuits with Embedded Cores” by Whetsel, published in the1997 IEEE International Test Conference proceedings.

With the modifications described and shown in FIG. 25B, the TAP is seento provide the same signal types as that seen in the controller of FIG.15A. For example in comparing FIGS. 25B and 15A it is seen that PEIrelates to TEI, PEO relates to TEO, TDO1 relates to SDO1, TDI1 relatesto SDI1, TMS relates to TPI, TCK relates to TCI, TDI relates to SDI, andTDO relates to SDO. Further it is seen that the operation of the TAP ofFIG. 25B and controller of FIG. 15A is similar. For example, (1) the TAPis enabled and disabled by the PEI signal, as the controller is enabledand disabled by the TEI signal, (2) the TAP shifts data from TDI to TDOin response to TMS and TCK, as the controller shifts data from SDI toSDO in response to TPI and TCI, (3) the TAP is initialized at reset toexclude a TDO1 to TDI1 scan path from the TDI and TDO scan path, as thecontroller is initialized at reset to exclude a SDC1 to SDI1 scan pathfrom the SDI and SDO scan path, (4) the TAP's instruction register canbe loaded with control to include a TDO1 to TDI1 scan path in the TDIand TDO scan path, as the controller's test control register can beloaded with control to include a SDO1 to SDI1 scan path in the SDI andSDO scan path, and (5) the TAP's instruction register can be loaded withcontrol to exclude a TDO1 and TDI1 scan path from the TDI and TDO scanpath, as the controller's test control register can be loaded withcontrol to exclude a SDO1 and SDI1 scan path from the SDI and SDO scanpath. A conventional TAP (i.e. the TAP of FIG. 25A) instruction registeris designed to include an update register as shown in FIG. 15B toprevent its control outputs from changing during shift operations.

Instruction Based Data Path Length Adjustment

The circuit of FIG. 25B can be generally viewed as a data path lengthadjustment circuit having first and second ports. The first port has anenable input (PEI) and first (TDI) and second (TDO) nodes forcommunicating data. The second port has an enable output (PEO) and first(TDO1) and second (TDI1) nodes for communicating data. The first port isenabled to communicate data between its first and second nodes if theenable input is high, and is disabled from communicating data if theenable input is low. The data communicated from the first and secondnodes of the first port passes through either an instruction register ora data register contained within the first port. The enable output ofthe second port comes from the instruction register of the first port.

A circuit connected to the second port is enabled to communicate datawith the first port if the enable output from the instruction registerof the first port has been set high in response to an instructionregister communication. In this case, communication occurs from thefirst node of the first port, through the instruction or data registerof the first port to the first node of the second port, through theconnected circuit to the second node of the second port, and from thesecond node of the second port to the second node of the first port. Acircuit connected to the second port is disabled from communicating datawith the first port if the enable output from the instruction registerof the first port has been set low in response to an instructionregister communication. In this case, communication occurs only from thefirst node of the first port, through the instruction or data registerof the first port, and to the second node of the first port.

If the circuit connected to the second port of the data path lengthadjustment circuit described above is another data path lengthadjustment circuit, it can be further connected at its second port toanother circuit, which may also be a data path length adjustmentcircuit, and so on. This concept of adjusting the length of a datacommunication by communication to an instruction register is not limitedto test data communication applications. It could be used in functionaldata communication applications as well. It is also independent of thephysical implementation of the data path length adjustment circuit,which could be realized as a sub-circuit within an integrated circuit orcore, or a device for use on a board or MCM. Also, while the data pathlength adjustment circuit has been described as having singular firstand second nodes at the first and second ports, a plurality of first andsecond nodes on each of the first and second ports is possible tosupport data path length adjustment of parallel data buses as well.Furthermore, the connectivity arrangement provided by the data pathlength adjustment circuit could be altered from the example givenwithout departing from the spirit and scope of the present invention.

U.S. Pat. Nos. 4,872,169 and 5,056,093, both by Whetsel, adjust thelength of scan paths. U.S. Pat. No. 4,872,169 adjusts the length of scanpaths by communication to a control bit contained within the scan path.U.S. Pat. No. 5,056,193 adjusts the length of scan paths bycommunication to a data register, following a first communication to aninstruction register. The data path length adjustment method describedabove occurs in response to only instruction register communication.

Operating State Machines with Shared I/O

In FIG. 26, the TAP of FIG. 25B and controller of FIG. 15A are connectedto allow both to coexists together in an integrated circuit or core. InFIG. 26, circuitry 2600 includes a test access port or TAP 2602 and acontroller 2604. TAP 2602 is like TAP 2530 and controller 2604 is likecontroller 1500. The similarities between the TAP and controller allowboth to share many of the same signals. For example, the TMS and TPIcontrol signals can be provided by a single shared TMS/TPI signal, theTCK and TCI clock signals can be provided by a single shared TCK/TCIsignal, the TDI and SDI data input signals can be provided by a singleshared TDI/SDI signal, the TDO and SDO data output signals can beprovided by a single shared TDO/SDO signal, the TDO1 and SDO1 dataoutput signals can be provided by a single shared TDO1/SDO1 signal, andthe TDI1 and SDI1 data input signals can be provided by a single sharedTDI1/SDI1 signal. The advantage of sharing these signals is that itreduces the number of integrated circuit pads, such as 2610, required toaccess the TAP or controller at the integrated circuit level, and alsoreduces wiring interconnect between integrated circuit level TAPs andcontrollers and embedded core level TAPs and controllers.

In FIG. 26, the PEI and TEI signals are not shared. This allows the TAPand controller to be enabled or disabled individually. If neither theTAP or controller is being accessed, the PEI and TEI signals will be setto disable them. If the TAP is being accessed, the PEI signal willenable the TAP and the TEI signal will disable the controller. If thecontroller is being accessed, the TEI signal will enable the controllerand the PEI signal will disable the TAP. The PEO and TEO outputs fromthe TAP and controller respectively, are also not shared to allowindividual control outputs for setting the PEI and TEI inputs ofembedded, lower level TAPs and controllers. When the TAP is enabled byPEI, buffers are enabled to allow the TAP to output on the sharedTDO/SDO and TDO1/SDO1 outputs. Likewise, when the controller is enabledby TEI, buffers are enabled to allow the controller to output on theshared TDO/SDO and TDO1/SDO1 output.

It is important to see in the arrangement of FIG. 26 that two statemachines, i.e. TAP and controller, are connected together using sharedinputs and outputs. It is further seen that each state machine can beindividually enabled to operate using the shared inputs and outputs toperform a function.

Architecture Supporting Hierarchically Arranged IEEE 1149.1 TAPs

When the controller is enabled and the TAP is disabled, the controlleroperates as if the TAP were not present and in all the arrangementspreviously described in FIGS. 17, 18, and 19. For example, when thecontroller is enabled and the TAP is disabled, the controller canoperate in the hierarchical arrangement of FIG. 17 to enable and connectup with lower level controllers. When the TAP is enabled and thecontroller is disabled, the TAP operates in a very similar way aspreviously described for the controllers in FIG. 17. For example, if theshared TAP and controller signals of FIG. 26 were substituted for thecontroller signals in FIG. 17, and if “integrated circuit TAP”, “Core 1TAP within integrated circuit”, and “Core 2 TAP within Core 1” weresubstituted for “integrated circuit Controller”, “Core 1 Controllerwithin integrated circuit”, and “Core 2 Controller within Core 1”,respectively, the process and description of hierarchically selecting alower level TAP by scanning a higher level TAP would follow closely thatgiven for the controller. Summarizing, the process would be to scan theinstruction register of the highest level TAP to enable a lower levelTAP, then scanning through both instruction registers of both TAPs tocontinue enabling further lower level TAPs or to load a test instructionto execute in both TAPs.

Known operations performed by TAPs in integrated circuits and coresinclude; (1) testing the interconnects between plural integratedcircuits on a board and plural cores within an integrated circuit, (2)testing circuitry contained within an integrated circuit or core, and(3) executing emulation and debug functions of circuitry containedwithin an integrated circuit or core. The ability to hierarchicallyaccess the TAPs within integrated circuits and cores, as shown in FIG.17, to perform these types of operations is therefore an importantaspect of the present invention.

What is claimed is:
 1. An integrated circuit comprising: a parallel scandistributor having a serial test data input and parallel test dataoutputs; a parallel scan collector having parallel test data inputs anda serial test data output; a first serial scan path having an inputcoupled with one of the parallel test data outputs, an output coupledwith one of the parallel test data inputs, and parallel functionaloutputs; a second serial scan path having an input coupled with one ofthe parallel test data outputs, an output coupled with one of theparallel test data inputs, and parallel functional inputs; andcombinational logic having functional inputs coupled with the functionaloutputs of the first serial scan path and functional outputs coupledwith the functional inputs of the second serial scan path.
 2. Theintegrated circuit of claim 1 in which the combinational logic hasplural functional inputs connected with one functional output of thefirst serial scan path.
 3. The integrated circuit of claim 1 in whichthe serial scan paths both contain scan cells with each scan cell havinga serial input coupled with a parallel output of the parallel scandistributor, a functional input, and a serial output that is connectedwith a parallel input of the parallel scan collector.
 4. The integratedcircuit of claim 3 in which the scan cells of the first serial scan patheach include a functional output connected to one of the parallelfunctional outputs.
 5. The integrated circuit of claim 1 in which theserial scan paths both contain scan cells with each scan cell having amultiplexer having a first input coupled to a parallel output of theparallel scan distributor, a second functional input, and an output, andeach cell having a memory having an input connected to the output of themultiplexer and an output coupled to a parallel input of the parallelscan collector.
 6. The integrated circuit of claim 5 in which the outputof the memory in each of the scan cells of the first serial scan pathincludes a functional output connected to one parallel functionaloutput.